Digital input/output system and method

• US 4,162,536 A
• Filed: 01/30/1978
• Issued: 07/24/1979
• Est. Priority Date: 01/02/1976
• Status: Expired due to Term

• Current Assignee: AEG Schneider Automation, INC. (Schneider Electric SE)
• Original Assignee: Gould Incorporated Modicon DIV
• Inventors: Morley, Richard E.
• Primary Examiner(s): Shaw, Gareth D.
• Assistant Examiner(s): Bartz, C. T.
• Application Number:
  US05/873,407
• Time in Patent Office: 540 Days
• Field of Search: 364/200 MS File, 364/900 MS File, 340/146.1 BA
• US Class Current: 714/18
• CPC Class Codes: G05B 19/054 Input/output
• CPC Class Codes: G05B 2219/1188 Detection of inserted boards, inserting extra memory, availability of boards
• CPC Class Codes: G05B 2219/13004 Programming the plc
• CPC Class Codes: G05B 2219/13142 Debugging, tracing
• CPC Class Codes: G05B 2219/15018 Communication, serial data transmission, modem
• CPC Class Codes: G05B 2219/15026 Detection of data transmission faults
• CPC Class Codes: G06F 13/38 Information transfer, e.g. on bus G06F13/14 takes precedence

Abstract

A parallel process controller capable of expandable, parallel operating multi-function control of processes. The process controller comprises programmable command memory modules, data memory modules, an input/output system, a programming panel, and a high speed data bus (N-bus).

The input/output system comprises input/output channels for intercommunication between the process controller and the external world. This intercommunication is repetitively updated for each input/output channel in an error-free manner that operates autonomously with respect to the remainder of the process controller. Each input/output channel incorporates a first dedicated area of a dedicated data memory module in which information is read and a second dedicated area of the data memory module in which information is written. The information read from the first dedicated area is transferred to external devices via a local modem-remote modem combination. Likewise, data written into the second dedicated area of the dedicated data memory module is transferred from the external device via the same remote modem-local modem combination.

Claims

1. A method of sending selected output data from a local location to a remote location and sending selected input data from the remote location to the local location, comprising the steps of:

(1) the local location selecting and sending output data to the remote location;

(2) the remote location receiving and echoing back to the local location the output data sent in step 1;

(3) the local location receiving and error-checking the echoed selected output data with that sent in step 1;

(4) if an error is detected in step 3, returning to step 1;

(5) if no error is detected in step 3, the local location generating and sending to the remote location a first signal indicating desired selected input data;

(6) the remote location receiving and echoing the received first signal to the local location;

(7) the remote location obtaining the desired selected input data;

(8) the local location receiving the echoed first signal and error-checking it with the first signal sent in step 5;

(9) if an error is detected in step 8, returning to step 5;

(10) if no error is detected in step 8, assuming at the local location that a successful transfer of output data from the local location to the remote location has occurred;

(11) the local location generating and sending a second signal to the remote location, the second signal requesting transferral of the input data obtained in step 7;

(12) the remote location receiving the second signal and sending to the local location the desired selected input data obtained in step 7;

(13) the local location receiving and storing the requested input data;

(14) the local location generating and sending a third signal requesting the transferral of the same input data requested in step 11 to the remote location;

(15) the remote location receiving the third signal and echoing back the desired selected input data to the local location;

(16) the local location receiving and storing the desired selected input data sent in step 15 and error-checking this data with that received in step 13;

(17) if an error is detected in step 16, the local location substituting the data received in step 16 for that received in step 13 and returning to step 14; and

(18) if no error is detected in step 16, the local location assuming a successful transfer of input data has occurred from the remote location to the local location and returning to step 1.

2. A method of sending data as defined in claim 1, wherein the local location at step 1 further generates a fourth signal indicating whether the output data there sent has been previously sent to the remote location and wherein the remote location generates a fifth signal along with the input data sent to the local location in step 12, the fifth signal indicating whether the desired selected input data has been previously sent to the local location.

3. A method of sending data as defined in claim 2, wherein the remote location obtains desired selected input data from the remote external world and obtains this data by generating a data request signal informing the remote external world to load data into a data buffer associated with the remote location.

4. A method of sending data as defined in claim 3, wherein no new input data is requested from the remote external world after receipt by the remote location of the second signal.

5. A method of sending data as defined in claim 4, wherein the local location communicates with a local external world and wherein the local location obtains the selected output data from the local external world and transfers to the local external world received selected input data from the remote external world.

6. A method of sending data as defined in claim 5, wherein the fourth signal is communicated from the remote location to the remote external world along with the output data received from the local location so as to indicate to the remote external world the status of the output data and further wherein the fifth signal is communicated from the local location to the local external world to indicate the status of the communicated input data received from the remote location.

7. A method of sending data as defined in claim 6, wherein the communicating of output data from the local external world to the local location and of input data from the local location to the local external world occurs for only a short predetermined length of time during which no transferral of data or signals from the local location to the remote location or from the remote location to the local location occurs.

8. A method of sending data as defined in claim 7, wherein the transferral of output data from the local external world to the local location and input data from the local location to the local external world occurs after step 18 but before returning to step 1.

9. A method of sending data as defined in claim 3, wherein the local location communicates with a local external world and wherein the local location obtains the selected output data from the local external world and transfers to the local external world received selected input data from the remote external world.

10. A method of sending data as defined in claim 9, wherein the fourth signal is communicated from the remote location to the remote external world along with the output data received from the local location so as to indicate to the remote external world the status of the output data and further wherein the fifth signal is communicated from the local location to the local external world to indicate the status of the communicated input data received from the remote location.

11. A method of sending data as defined in claim 10, wherein the communicating of output data from the local external world to the local location and of input data from the local location to the local external world occurs for only a short predetermined length of time during which no transferral of data or signals from the local location to the remote location or from the remote location to the local location occurs.

12. A method of sending data as defined in claim 11, wherein the transferral of output data from the local external world to the local location and input data from the local location to the local external world occurs after step 18 but before returning to step 1.

13. A method of sending selected output data from a local location to a remote location and sending selected input data from the remote location to the local location, for use of the output data by the remote external world and for use of the input data by the local external world comprising the steps of:

(1) the local location selecting and obtaining output data from the local external world;

(2) the local location entering a data output mode by generating a first header (Hφ

) including "output new word" data indicating whether the obtained output data from the local external world is new data;

(3) the local location sending the first header with the selected output data to the remote location;

(4) the remote location receiving and storing the selected output data and at least a portion of the first header including the "output new word" data and the selected output data;

(5) the remote location echoing the first header and the selected output data received in step 4 back to the local location;

(6) the local location receiving and error checking the echoed first header and echoed selected output data respectively with the first header and selected output data sent to the remote location in step 3;

(7) if an error is detected in step 6, returning to step 3;

(8) if no error is detected in step 6, the local location entering the output verify mode by generating a second header (H1) including data representing addressable desired input data to be sent from the remote location to the local location;

(9) the local location sending the second header to the remote location;

(10) the remote location receiving the second header and then allowing the stored output data and status of the "output new word" data received in step 4 to be used by the remote external world, the remote location storing at least the portion of the second header representing the address of the desired input data and obtaining from the remote external world the data at the desired address;

(11) the remote location echoing the received second header to the local location;

(12) the local location receiving the echoed second header and error checking it with the second header sent to the remote location in step 9;

(13) if an error is detected in step 12, returning to step 9;

(14) if no error is detected in step 12, assuming at the local location that a successful transfer of output data from the local location to the remote location has occurred and the local location entering the data input mode by generating a third header (H2);

(15) the local location sending the third header to the remote location;

(16) the remote location receiving the third header and echoing back to the local location at least the desired input data obtained from the remote external world in step 10 along with "input new word" data indicating whether the obtained input data from the remote external world is new;

(17) the local location receiving and storing the requested input data and the "input new word" data;

(18) the local location entering the data input verify mode by generating a fourth header (H3);

(19) the local location sending at least the fourth header to the remote location;

(20) the remote location receiving the fourth header;

(21) the remote location echoing back at least a portion of the fourth header to the local location along with the desired selected input data and the "new input word" data;

(22) the local location receiving and storing the desired selected input data and the "new input word" data sent in step 21 and error checking these data respectively with the data received in step 17;

(23) if an error is detected in step 22, the local location regarding the data received in step 22 as that received in step 17 and returning to step 18; and

(24) if no error is detected in step 22, the local location assuming a successful transfer of data has occurred from the remote location to the local location and allowing the local external world to use the input data and "new input word" data stored in step 22, and returning to step 1;

whereby output data is obtained from the local external world and is error-free transferred from the local location to the remote location for use by the remote external world with data indicating the newness of the output data and whereby input data is obtained from the remote external world and is error-free transferred from the remote location to the local location for use by the local external world with data indicating the newness of the input data.

14. A method of sending data as defined in claim 13, wherein the input data and output data respectively comprise P and Q addressable lines of data, where P and Q are positive integers.

15. A method of sending data as defined in claim 14, wherein the output data and input data comprise addressable lines of data which are sequentially and repetitively transferred according to steps 1-24.

16. A method of sending data as defined in claim 15, wherein the lines of output data and input data comprise an invariant number of binary bits.

17. A method of sending data as defined in claim 16, wherein the first, second, third and fourth headers each comprise a fixed number of binary bits.

18. A method of sending data as defined in claim 17, wherein each header precedes any output data or input data associated therewith.

19. A method of sending data as defined in claim 18, wherein arbitrary data is generated by the local location along with the third header (H2) and fourth header (H3) and wherein said arbitrary data is sent to the remote location with the third header and fourth header respectively.

20. A method of sending data as defined in claim 19, wherein the echoing of data from the remote location to the local location occurs while the remote location is receiving data from the local location.

21. A method of sending data as defined in claim 14, wherein the input data, output data, and first, second, third and fourth headers comprise binary bits.

22. A method of sending data as defined in claim 21, wherein the local location at step 1 repetitively sequentially selects one of the Q addressable output data lines and wherein the local location at step 8 repetitively sequentially selects one of the P addressable input data lines.

23. A method of sending data as defined in claim 22, wherein the first, second, third and fourth headers comprise at least 16 digital bits, with at least one bit for the state of the "output new word" data or "input new word" data, at least one bit for the complement of the "output new word" data or "input new word" data, at least four bits for the line number of the selected input data line or of the selected output data line, at least four bits for the complement of the line number of the selected input data line or of the selected output data line, at least two bits for a code representing the first, second, third or fourth header, at least two bits for the complement of the header code, and at least one synchronization bit.

24. A method of sending data as defined in claim 14, wherein the local location at step 1 repetitively sequentially selects one of the Q addressable output data lines and wherein the local location at step 8 repetitively sequentially selects one of the P addressable input data lines.

25. A method of sending data as defined in claim 14, wherein integer P equals integer Q.

26. A method of sending data as defined in claim 13, wherein at step 10 the remote location error-checks the received second header and only allows the stored output data received in step 4 to be used by the remote external world if no error is detected in the second header.

27. A method of sending data as defined in claim 26, wherein at step 10 the remote location generates a "data valid" signal when no error is detected in the second header so as to allow the stored output data received in step 4 to be used by the remote external world.

28. A method of sending data as defined in claim 26, wherein at step 10 the remote location obtains data from the external remote world by setting a request new input data signal and wherein this signal is cleared at the remote location in step 16.

29. A method of sending data as defined in claim 13, wherein the echoing of data from the remote location to the local location occurs while the remote location is receiving data from the local location.

30. A method of sending output data from a local location to a remote location and sending input data from a remote location to a local location, for use of the output data by the external remote world and for use of the input data by the external local world, comprising the steps of:

(1) the local location selecting and obtaining output data from the local external world;

(2) the local location generating a first header (Hφ

);

(3) the local location sending the first header with the output data to the remote location;

(4) the remote location receiving the first header and output data and storing at least a portion of the output data;

(5) the remote location echoing the first header and the output data received in step 4 back to the local location;

(6) the local location receiving the echoed first header and output data and error-checking this data respectively with the first header and output data sent in step 3;

(7) if an error is detected in step 6 returning to step 3;

(8) if no error is detected in step 6, the local location generating a second header (H1) including data representing the location of input data to be sent from the remote location to the local location;

(9) the local location sending the second header to the remote location;

(10) the remote location receiving the second header, allowing the stored output data received in step 4 to be used by the remote external world, and obtaining and storing from the remote external world input data represented by at least a portion of the second header;

(11) the remote location echoing the received second header to the local location;

(12) the local location receiving the second header and error-checking it with that sent in step 9;

(13) if an error is detected in step 12 returning to step 9;

(14) if no error is detected in step 12 assuming at the local location that a successful transfer of output data from the local location to the remote location has occurred and generating a third header (H2);

(15) the local location sending the third header to the remote location;

(16) the remote location receiving the third header and echoing back to the local location at least a portion of the received third header and sending the input data represented by at least a portion of the second header obtained fromthe remote external world in step 10 to the local location;

(17) the local location receiving and storing the input data;

(18) the local location generating a fourth header (H3);

(19) the local location sending at least the fourth header to the remote location;

(20) the remote location receiving the fourth header;

(21) the remote location echoing back at least a portion of the fourth header to the local location along with input data represented by at least a portion of the second header;

(22) the local location receiving and storing the input data sent in step 21;

(23) the local location error-checking the input data received in step 22 with that received in step 17;

(24) if an error is detected in step 23, the local location substituting the received input data in step 22 for that received in step 17 and returning to step 18; and

(25) if no error is detected in step 23, the local location assuming a successful transfer has occurred of input data from the remote location to the local location and allowing the local external world to use the input data stored in step 22.

31. A method of sending output data and input data defined in claim 30, wherein the output data and input data comprise addressable lines of data which are sequentially and repetitively transferred according to steps 1-25.

32. A method of sending output data and input data as defined in claim 31, wherein the lines of output data and input data comprise an invariant number of binary bits.

33. A method of sending output data and input data as defined in claim 32, wherein the generating of the first header (Hφ

) includes the generation of "output new word" data representing the first transferral of output data from the local location to the remote location and wherein the remote location at step 17 in addition to echoing back at least a portion of the received third header and sending the desired input data obtained from the remote external world in step 10 further generates and sends "input new word" data representing the first sending of this particular input data to the local location and wherein the remote location allows the remote external world to sense the "output new word" data so as to inform the remote external world that the associated output data is new output data and wherein the local location allows the local external world to sense the "input new word" data so as to inform the local external world that the received input data is new.

34. A method of sending output data and input data as defined in claim 33, wherein the remote location allows the stored output data received in step 4 to be used by the remote external world in step 10 by generating a "data valid" signal at the remote location.

35. A method of sending output data and input data as defined in claim 30, wherein the first, second, third and fourth headers each comprise a fixed number of binary bits.

36. A method of sending output data and input data as defined in claim 35, wherein each header precedes any output data or input data associated therewith.

37. A method of sending output data and input data as defined in claim 36, wherein arbitrary data is generated by the local location along with the third header (H2) and fourth header (H3) and wherein said arbitrary data is sent to the remote location with the third header and fourth header respectively.

38. A method of sending output data and input data as defined in claim 37, wherein the output data and input data comprise an equal number of binary bits and wherein the arbitrary data generated with the second header (H1) and third header (H2) comprise binary bits equal in number to the output data and input data.

39. A method of sending output data and input data as defined in claim 38, wherein the echoing of data from the remote location to the local location occurs while the remote location is receiving data from the local location.

40. A method of sending output data and input data as defined in claim 30, wherein the echoing of data from the remote location to the local location occurs while the remote location is receiving data from the local location.

41. An input/output system for transferring information to and from a remote external device comprising:

(A) an input/output memory for storage of input data received from the remote external device and output data for transferral to the remote external device;

(B) at least one input/output channel interconnected with said input/output memory for receiving from the external device input data and for transferring to the external device output data, said input/output channel incorporating;

(1) a local modem having,

(a) header generating means for generating signals representing the current operating state of the input/output channel,

(b) signal transferring means for receiving and transferring the output data to the remote external device and for receiving and transferring input data received from the remote external device to the iput/output memory, and

(c) error-checking means for insuring the proper transferral and receipt of output data and input data to and from the remote external device;

(2) data communications means interconnected with the local modem for transferring output data and for receipt of input data; and

(3) a remote modem having,

(a) means for receiving header signals and output data transferred by the local modem through the data communication means to the remote modem and for transferral of this output data to the remote external device when verification of error-free transferral of said output data is ascertained,

(b) means for receiving input data from the remote external device, and

(c) signal transferring means for transferring input data and echoing of received output data and header signals to the local modem,

wherein the header generator means of the local modem generates a first header (Hφ

), said header transferred with output data received from the input/output memory to the remote modem, said remote modem receiving and storing at least a portion of the transferred output data and echoing back at least a portion of the first header and transferred output data back to the local modem, the error-checking means of the local modem comparing the received header against that transferred and the received output data with that transferred by the local modem, and again transferring the first header with the same output data if any error is detected between the echoed first header or echoed output data with that transferred by the local modem to the remote modem, and if no error is detected, the header generator means generating a second header (H1) including data representing the location of the desired input data to be obtained by the remote modem from the remote device, the remote modem receiving the incoming second header with the data representing the address of desired input data, the signal transferring means allowing the received output data to be transferred to the remote external device upon receipt of the second header, and the signal transferring means echoing back the second header to the local modem, the error-checking means of the local modem comparing the received second header with the second header sent to the remote modem and if an error is detected causing the signal transferring means of the local modem to re-transfer the second header to the remote modem, and if no error is detected assuming that a successful transfer of output data has occurred, the local modem then entering a data input cycle by generating a third header (H2) with data representing the location of desired input data sent with the second header, the remote modem receiving the third header and echoing back to the local modem the third header along with the specified input data, the local modem receiving the third header and the input data and storing the input data, the local modem generating a fourth header (H3) with data requesting the same input data specified in the second header, the remote modem receiving the fourth header and echoing back at least a portion of the fourth header with the data located in the specified location, the local modem error-checking the fourth header and input data respectively with the fourth header transferred by the local modem to the remote modem and with the input data received immediately prior to the presently received input data and if any error is detected in either the fourth header or the input data respectively with the fourth header transferred to the remote modem or with the previously received input data, causing the most recently received input data to be stored by the local modem and again generating and sending the fourth header to the remote modem, and if no error is detected in either the fourth header or the received input data, assuming that a successful transferral of input data has occurred and allowing the input/output memory to obtain the latest received input data from the local modem.

42. An input/output system as defined in claim 41, wherein the input data comprises P lines of data and the output data comprises Q lines of data, P and Q being positive integers and wherein the local modem sequentially transfers the Q output lines to the remote modem and wherein the local modem header generator means in at least the second header includes data representing the sequential locations of the P input lines and wherein the local modem sequentially and repetitively transfers the Q output lines to the remote modem and sequentially requests the receipt of the P input lines from the remote modem.

43. An input/output system as defined in claim 42, wherein P and Q are the same integer.

44. An input/output system as defined in claim 43, wherein the input data and output data both comprise an equal and invariant number of binary bits.

45. An input/output system as defined in claim 44, further comprising:

(C) means for generating a repetitive timing and control signal communicating with the input/output channel for causing data to be transferred to and from the input/output channel and the input/output memory for a short predetermined length of time after receipt of said timing and control signal other than when the input/output memory is communicating with the input/output channel, wherein the input/output memory may be accessed by the local external world at all times other than such short predetermined length of time when the input/output memory is communicating with the input/output channel.

46. An input/output system as defined in claim 45, wherein the local modem header generator means further generates arbitrary data along with the third and fourth headers for transferral to the remote modem.

47. An input/output system as defined in claim 46, wherein the arbitrary data generated by the local modem header generator means along with the third and fourth headers each comprise an invariant number of binary bits equal to the number of binary bits associated with the input data and output data.

48. An input/output system as defined in claim 47, wherein the remote modem signal transferring means echoes the header and data to the local modem while the remote modem is in the process of receiving the header and data.

49. An input/output system as defined in claim 41, wherein the remote modem signal transferring means echoes the header and data to the local modem while the remote modem is in the process of receiving the header and data.

50. An input/output system comprising:

(A) an input/output memory for the storage and receipt of input data and output data; and

(B) at least one input/output channel interconnected with the input/output memory for transferring output data from the input/output memory and for receiving input data for storage by the input/output memory, the input/output channel incorporating;

(1) a local modem having,

(a) means for selecting and receiving output data from the input/output memory,

(b) means for generating header signals indicating the state of data transferral to and from the local modem,

(c) data transferring and receiving means for transferring the output data and header signals and for receiving the input data and header signals, and

(d) error-checking means for insuring the proper transferral and receipt of output data and input data to and from the local modem;

(2) data communication means interconnected with the local modem for transferring from the local modem header signals and output data and for receiving at the local modem header signals and input data; and

(3) a remote modem having,

(a) means for receiving output data and header signals from the local modem through the data communication means, and

(b) data transferring means for echoing received output data and header signals and for transferring input data and header signals to the local modem through the data communication means;

wherein, (1) the local modem sends selected output data to the remote modem;

(2) the remote modem receives and echoes back to the local modem the output data;

(3) the local modem receives and error-checks the echoed selected output data with that sent in step 1;

(4) if an error is detected in step 3, the local modem returning to step 1;

(5) if no error is detected in step 3, the local modem generating and sending to the remote modem a first header signal indicating desired selected input data;

(6) the remote modem receiving and echoing the received first header signal to the local modem;

(7) the remote modem obtaining the desired selected input data from the remote external world;

(8) the local modem receiving the echoed first header signal and error-checking it with the first header signal sent in step 5;

(9) if an error is detected in step 8, returning to step 5;

(10) if no error is detected in step 8, assuming at the local modem that a successful transfer of output data from the local modem to the remote modem has occurred;

(11) the local modem generating and sending a second header signal to the remote modem, the second header signal requesting transferral of the input data obtained in step 7;

(12) the remote modem receiving the second header signal and sending to the local modem the desired selected input data obtained in step 7;

(13) the local modem receiving and storing the requested input data;

(14) the local modem generating and sending to the remote modem a third header signal requesting the transferral of the same input data requested in step 11;

(15) the remote modem receiving the third header signal and echoing back the desired selected input data to the local modem;

(16) the local modem receiving and storing the desired selected input sent in step 15 and error-checking this data with that received in step 13;

(17) if an error is detected in step 16, the local modem substituting the data received in step 16 for that received in step 13 and returning to step 14; and

(18) if no error is detected in step 16, the local modem assuming a successful transfer of input data has occurred from the remote modem to the local modem and returning to step 1.

51. An input/output system as defined in claim 50, wherein the local modem header generating means further comprises means at step 1, for generating a "new output" signal indicating whether the output data there sent has been previously sent to the remote modem.

52. An input/output system as defined in claim 51, wherein the remote modem further comprises a data buffer communicating with the data receiving means and data transfer means, and wherein the remote modem further comprises means for obtaining the desired selected input data from a remote external world by generating a data request signal informing the remote external world to load data into the data buffer.

53. An input/output system as defined in claim 52, wherein the input/output memory communicates with a local external world and wherein the input/output memory obtains the selected output data from the local external world and transfers to the local external world received selected input data from the remote external world.

54. An input/output system as defined in claim 53, further comprising first means for communicating the "new output" signal from the remote modem to the remote external world along with the output data received from the local modem so as to indicate to the remote external world the status of the output data and further comprising second means for communicating the "new input" signal from the input/output memory to the local external world to indicate the status of the input data received from the remote modem.

55. An input/output system as defined in claim 54, further comprising:

(A) means for generating a repetitive timing and control signal communicating with the input/output channel causing data to be transferred to and from the input/output channel and the input/output memory for a short predetermined length of time after receipt of the timing and control signal other than when the input/output memory is communicating with the input/output channel, wherein the input/output memory may be accessed by the local external world at all times other than such short predetermined length of time when the input/output memory is communicating with the input/output channel.

56. An input/output system for transferring information to and from the remote external world and local external world comprising:

(A) an input/output memory for the storage and receipt of input data as P input lines from the remote external world and output data as Q output lines from the local external world, P and Q being positive integers, the memory having means for generating "new output word" data indicating the newness status of an output data line, the "new output word" data having a first state when the output data line is first received by the memory and having a second state after the output data line is transferred from the memory; and

(B) at least one input/output channel interconnected with said input/output memory for processing, isolating and receiving from the remote external world P lines of input data and transferring to the remote external world Q lines of output data, said input/output channel incorporating;

(1) a local modem having,

(a) means for sequentially receiving, processing and isolating the Q output data lines of the input/output memory,

(b) header generator means for generating header data, including the "new output word" data, representing the current operating state of the input/output channel,

(c) data transferring and receiving means for transferring the processed and isolated Q output data lines and the header data, and for receiving the P input data lines and header data, and

(d) error-checking means for insuring the proper transferral and receipt of output data and input data to and from the remote external world;

(2) data communications means interconnected with the local modem for transferring from the local modem and receiving at the local modem data including the transferral of header data, and Q output data lines and for receiving header data, and P input data lines; and

(3) a remote modem having,

58. An input/output system as defined in claim 56, further comprising:

(C) means for generating a repetitive timing and control signal communicating with the input/output channel for causing information to be transferred to and from an input/output channel and the input/output memory for a short predetermined length of time after receipt of the timing and control signal other than when the input/output memory is communicating with the input/output channel, whereby said input/output memory may be accessed at all times by the local external world other than said short predetermined length of time when the input/output memory is communicating with the input/output channel.

60. An input/output system as defined in claim 58, wherein the "data valid" signal is cleared by the remote modem after receipt of the first header data.

57. (a) means for receiving, processing and isolating data transferred by the local modem through the data communications means to said remote modem and transferral of each of the Q output lines of isolated and processed data to the remote external world when verification of error-free transferral of each output data line is ascertained,

(b) a header data storage, decoding, and error-checking means for storing the transferred header data and for error-checking the contents of the header data,

(c) means for sequentially receiving, processing and isolating the P input data lines from the external remote world,

(d) means for generating a "data valid" signal and for generating and inserting into a header data a "new input word" data indicating the newness status of an input data line, having a first state when an input data line is first received by the remote modem from the remote external world and having a second state after the input data line is transferred to the local modem;

and

(e) data transferring means for echoing the received Q output data lines and header data to the local modem and for transferring the P input data lines received from the external remote world and header data to the local modem after a "data valid" signal is generated;

wherein the header generator means of the local modem initiates an output transferral state by generating a first header data (Hφ

) including the "new output word" data from the input/output memory representing the newness status of the output data line, the header data transferred with the selected line of output data to the remote modem, the remote modem transferring means echoing the transferred line of output data back to the local modem along with the first header data, the error-checking means of the local modem comparing the received header data against that transferred and the received line of output data with that transferred, and if an error is detected causing the retransferral of the first header data and output data line to the remote modem, and if no error is detected the header generator means generating a second header data (H1) including an input line number associated with one of the P input data lines to be transferred by the remote modem to the local modem, the remote modem receiving and decoding the incoming second header data and if no error is detected in the second header generating a "data valid" signal allowing the transferral of the received output data to the remote external world, the remote modem data transferring means echoing back the second header data to the local modem, the error-checking means of the local modem comparing the received second header data with the second header data sent to the remote modem and if an error is detected causing the local modem to re-transfer the second header data to the remote modem, and if no error is detected assuming that a successful transferral of the selected Q output data line has occurred, the local modem header generator means then generating a third header data (H2) including the input data line number previously sent to the remote modem, the local modem transferring means transferring the third header data to the remote modem, the remote modem decoding this third header data and transferring the selected P input data line obtained from the remote external world to the local modem along with the third header data including the "new input word" data where it is stored by the local modem data transferring and receiving means, the local modem entering a data input verify state by the header generator means then generating a fourth header data (H3), the local modem transferring means transferring the fourth header data to the remote modem, the remote modem decoding the fourth header data and reloading the selected input data line from the remote external world and transferring it back to the local modem along with the fourth header data with the "new input word" data, the error-checking means of the local modem comparing the received selected P input data line with that previously received with the third header data and, if no error is detected, transferring the input data line from the local modem to the input/output memory and the local modem then incrementing to the next sequential output data line and returning to the output transferral state, and if an error is detected causing a re-transferral of the fourth header data to the remote modem and consequently causing the remote modem to re-transfer the selected input data line to the local modem until such time that the local modem error-checking means obtains an error-free transferral of the input data line;

whereby the input/output channel continuously transfers Q output data lines from the local modem to the remote modem with error-checking thereof for transferral to the remote external world and transfers P input data lines from the remote modem to the local modem with error-checking thereof for transferral to the input/output memory and thus to the local external world.

59. An input/output system as defined in claim 57, wherein the data communications means comprises a coaxial cable.