Auxiliary ROM memory system

• US 4,141,068 A
• Filed: 03/24/1977
• Issued: 02/20/1979
• Est. Priority Date: 03/24/1977
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Nelson, Frank M., Mager, George E., Reid, Steven L., Richardson, Philip, Post, Donald S., Rochat, Vernon E.
• Primary Examiner(s): Zache, Raulfe B.
• Application Number:
  US05/780,875
• Time in Patent Office: 698 Days
• Field of Search: 364/200 MS File, 364/900 MS File
• US Class Current: 711/103
• CPC Class Codes: G06F 12/0638 Combination of memories, e.g. ROM and RAM such as to permit replacement or supplementing of words in one module by words in another module address formation of the next microinstruction G06F9/26; masking faults in memories by using spares or by reconfiguring G11C29/70
• CPC Class Codes: G06F 8/66 of program code stored in read-only memory [ROM]

Abstract

An auxiliary ROM memory system which is hierarchied for providing for the contingency of additional read-only memory control program storage requirements in excess or in lieu of the predetermined ROM memory provided on-board a microprocessor based central processing unit module, and a read-only memory altering capability utilizing programmable read-only memory to expedite the implementation/installation of changes to the ROM bit patterns. The alterable PROM storage comprises bulk PROM memory including a first PROM set that is mutually exclusive as to existing on-board ROM memory for addressably branching to code extensions and/or in-line code insertions, and/or a second PROM set that is mutually inclusive as to existent on-board and contingent ROM memory for decodably addressing large-scale code overlays thereto. In addition, the alterable PROM storage comprises patch PROM for addressing, through multi-leveled decoding, small-scale code overlays to the on-board and contingent ROM memory for single in-line bit pattern alterations. Conflicting memory requests involving addresses recognized by more than one of the supra memory categories, when enabled, are presented to a predetermined hierarchy of memory precedences for resolution thereof. Each of the enumerated memory categories of the auxiliary ROM memory system may be operative to have its population incremented or decremented without invalidating the above hierarchy of addressing.

Claims

1. A system for providing hierarchied auxiliary read-only memory in addition to read-only memory on-board a central processing unit module comprising:

(a) memory means for providing a plurality of memory categories including permanent read-only memory and alterable programmable read-only memory for data storage in excess or in lieu of on-board read-only memory and for implementation and installation of changes to on-board read-only memory respectively; and

(b) decoder means for recognition of addresses for accessing a given memory category of said memory means according to a predetermined hierarchy when the given accessing address falls within more than one or more overlapping subordinated address ranges for the memory categories of said memory means.

2. A hierarchied auxiliary memory system having structured ROM for use through a system bus as an adjunct to ROM on-board a central processing unit module for storage of instruction code comprising:

(a) Contingent ROM memory means operatively coupled through the system bus to the central processing unit module for permanent storage of code in excess of or in lieu of that residing in the on-board ROM and said contingent ROM memory means;

(b) Alterable PROM memory means operatively coupled through the system bus to the central processing unit module for storage of code implementation and installation of code changes to on-board ROM; and

(c) Address Decoder means operatively coupled through the system bus to the central processing unit module for receipt of addresses therefrom for controlling the accessing of instruction code in said Contingency ROM memory means and said Alterable PROM memory means, and for ordered resolution according to a predetermined hierarchy for accessing precedence when memory ranges thereof overlap and therefore conflict by subordinating the former to the latter.

3. The hierarchied auxiliary memory system of claim 2 wherein said contingency ROM memory means comprises:

(a) Address Buffer means operative to receive addresses on the system bus from the CPUM for signal driving and corrective biasing therefor for correlative matching of signal levels;

(b) Permanent ROM storage means having addressing ranges that are transferably equivalent to ROM on board the CPUM and operative to receive driven address signals from said Address Buffer means for accessing instruction data sets mask stored therein in a plurality of partitions for transmittal on the system bus; and

(c) Instruction multiplexer means operative to receive instruction data from more than one partition of said permanent ROM storage means for selection of a instruction data set from one of the presented partitions according to a predetermined code of addresses received on the system bus from the CPUM for transmittal through the system bus to the CPUM.

4. The hierarchied auxiliary memory system of claim 3 wherein said address buffer means comprises a plurality of gating means operative to receive each of the addresses separately on the system bus for the driving thereof, and a plurality of resistive means operative to receive each of the driven addresses separately for biasing thereof.

5. The hierarchied auxiliary memory system of claim 4 wherein each of said plurality of gating means is a positive logic And gate having commonly tied inputs.

6. The hierarchied auxiliary memory system of claim 4 wherein each of said plurality of resistive means is a resistive element having a controlled potential dropped across thereof.

7. The hierarchied memory system of claim 3 wherein said permanent ROM storage means comprises a quad of memory block means operative to receive the driven address signals for service as the memory partitions for use maximization of the limited input/output ports into the system bus for outputing a unique set of instruction data from each of said quad of memory block means.

8. The hierarched memory system of claim 7 wherein each of said quad of memory block means of said permanent ROM storage means include a plurality of mask programmable read-only-memory means each operative to receive a first portion of the driven addresses on the system bus at its addressing inputs and a second portion of the driven addresses on the system bus at its chip select inputs for unitary enabling thereof at any given time as accesses of instruction data onto the system bus.

9. The hierarched memory system of claim 7 wherein said instruction multiplexer means further includes a plurality of resistive means operative to receive each of the accessed instruction data separately on the system bus from said quad of memory block means for biasing thereof.

10. The hierarchied memory system of claim 9 wherein each of said plurality of resistive means is a resistive element having a controlled potential dropped across thereof.

11. The hierarchied memory system of claim 7 wherein said instruction multiplexer means further includes a pair of multiplexer block means each operative to receive a unique duality of accessed instruction data sets from said quad of memory block means for selective routing of one of the duality of accessed instruction data sets therethrough.

12. The hierarchied memory system of claim 11 wherein each of said pair of multiplexer block means further includes a pair of multiplexer means each operative to receive one part of each of the unique duality of accessed instruction data sets for alternative selection and strobed throughputing according to a subset of the driver address signals.

13. The hierarchied memory system of claim 3 further including address tri-state driver means operative to receive address signals on the system bus from the CPUM for output in a tri-state mode as driven signals for receipt by said address buffer means.

14. The hierarchied memory system of claim 13 wherein said address tri-state driver means is operative to have its control line grounded for continuous operation thereof.

15. The hierarchied memory system of claim 3 further including instruction tri-state driver means operative to receive an instruction data set from said instruction multiplexer means for output in a tri-state mode as biased driven signals on the system bus to the CPUM.

16. The hierarchied memory system of claim 15 wherein said instruction tri-state driver means is operative to have its control line enabled by receipt of a memory read signal on the system from the CPUM for enabled operation thereof.

17. The hierarchied auxiliary memory system of claim 2 wherein said alterable PROM memory means comprises:

(a) Bulk PROM means operative to receive accessing addresses through the system bus from the central processing unit module for accessing instruction code programmably stored therein according to mutuality of address assigning for extensions, insertions, and large-scale overlay to code in board ROM and said contingency ROM memory means;

(b) Patch PROM means operative to receive accessing addresses through the system bus from the central processing unit module for accessing instruction code programmably stored therein for single in-line bit pattern alterations through small-scale code overlay to code in the on-board ROM and said contingency ROM memory means.

18. The hierarchied auxiliary memory system of claim 17 wherein said patch PROM means further includes programmable read-only memory means operatively coupled to the system bus for storage of instruction code for transmittal upon command to the central processing module.

19. The hierarchied auxiliary memory system of claim 18 wherein said address decoding means further includes:

(a) a first-level decoding means for partitioning the programmable read-only memory means of said patch PROM means into a predetermined finite number of locations, and operative to receive a first portion of the address on the system bus for selecting a unique location from the set of locations through the generation of a psuedo address therefor; and

(b) second-level decoding means operative to receive the psuedo address from said first-level decoding means for pointing to a particular group as a subset of the selected location, and operative to receive a second portion of the address on the system bus for identifying a byte pointer to a multi-byte segment of the particular group for said patch PROM means.

20. The hierarchied auxiliary memory system of claim 19 wherein said second-level decoding means of said address decoding means further includes means operative to receive a third portion of the address on the system bus for pointing to a unitary byte to be selected from the multi-byte segment of the particular group for said patch PROM means.

21. The hierarchied auxiliary memory system of claim 19 wherein said first-level decoding means of said address decoding means further includes means operative upon receipt of an address on the system bus within the effective address range of said Bulk PROM means for generating a control signal representative thereof.

22. The hierarchied auxiliary memory system of claim 21 wherein said second-level decoding means further includes means for interpreting a predetermined bit position of the byte pointer to the multi-byte segment as indicating that the effective address range of said patch PROM means is being accessed for generating a control signal representative thereof, for generating a patch address set indicating a unique instruction data set to be accessed, and for generating a pair of control signals indicating the portion of said patch PROM means to be accessed by the patch address set.

23. The hierarchied auxiliary memory system of claim 21 wherein said unitary byte selection means of said second-level decoding means is further operative to hierarchically resolve conflicts as between signals from said first and second level decoding means indicating that the requesting address overlaps effective address ranges for both said bulk and patch PROM means by subordinating the former to the latter respectively.

24. The hierarchied auxiliary memory system of claim 22 wherein said programmable read-only memory means of said patch PROM means further includes a plurality of PROM means operative to receive the patch address set from said second-level decoding means for accessing one predetermined set thereof as selected by the pair of patch PROM portion control signals from said second-level decoding means for generation of an instruction set on the system bus.

25. The hierarchied auxiliary memory system of claim 17 wherein said bulk PROM means further includes:

(a) programmable read-only memory means operatively coupled to the system bus for storage of instruction code for transmittal upon command to the central processing unit module; and

(b) address decoding means operatively coupled to receive address signals through the system bus from the central processing unit module for accessing instruction code from said programmable read-only memory means according to a mutuality of assigned addresses for changing the on-board ROM and said contingency ROM memory means.

26. The hierarchied auxiliary memory system of claim 25 wherein said address decoding means further includes means for specifying said programmable read-only memory means of said bulk PROM means into a predetermined address range area and designating a subset of these address range areas as address effective areas and for allowing one or more of the address effective areas to contain all or part of the instruction code.

27. The hierarchied auxiliary memory system of claim 25 wherein said address decoding means further includes means for instituting the mutuality of assigned addresses of said bulk PROM means in a mutually exclusive mode for extensions and insertions of code to on-board ROM.

28. The hierarchied auxiliary memory system of claim 25 wherein said address decoding means further includes means for instituting the mutuality of assigned addresses of said bulk PROM means in a mutually inclusive mode for large-scale code overlay on-board ROM.

29. The hierarchied auxiliary memory system of claim 25 further includes a patch memory means operatively coupled to the system bus for single in-line bit pattern alterations to read-only memory on-board the central processing unit module for allowing said programmable read-only memory means of said Bulk PROM means to be accessed through said address decoding means by addresses patched into the on-board ROM by said patch memory means.

30. The hierarchied auxiliary memory system of claim 27 wherein the mutually exclusive means of said address decoding means for said bulk PROM means acts to provide large-scale overlays of code to on-board ROM through branching of addresses.

31. The hierarchied auxiliary memory system of claim 28 wherein the mutually inclusive means of said address decoding means for said bulk PROM means acts to provide extension and insertions of code to on-board ROM through decoding of addressing.

32. The hierarchied auxiliary memory system of claim 26 wherein said specifying means of said address decoding means further includes means for constraining the access of all the instruction codes to be from one predetermined address effective area in said programmable read-only memory means of said bulk PROM means.

33. The hierarchied auxiliary memory system of claim 26 wherein said specifying means of said address decoding means further includes means for constraining access of all the instruction codes to be from more than one of the address effective areas in said programmable read-only memory means of said bulk PROM means.

34. The hierarchic auxiliary memory system of claim 25 wherein said programmable read-only memory means of said bulk PROM means further includes a plurality of PROM means operative to receive address signals on the system bus from the CPUM for accessing one predetermined set thereof as selected by the given address for generation of an instruction data set on the system bus.

35. The hierarchied auxiliary memory system of claim 34 wherein said programmable read-only memory means of said bulk PROM means further includes demultiplexer means operative to receive a predetermined portion of the address signals on the system bus from the CPUM for selecting the set of PROM means out of said plurality of PROM means to be chip enabled for addressing thereof.

36. The hierarchied auxiliary memory system of claim 35 wherein said demultiplexer means of said programmable read-only memory means of said bulk PROM means further includes means operative to receive a bulk PROM control signal from said address decoding means for allowing said demultiplexer means to chip enable a selected set of said plurality of PROM means, and operative to receive a patch PROM control signal from said address decoding means for hierarchically disabling and thereby subordinating the bulk PROM control signal.

37. The hierarchied auxiliary memory system of claim 19 wherein said first-level decoding means further includes a first pair of programmable read-only memory means operative to receive address signals on the system bus from the CPUM for decodably generating a psuedo address set to said second-level decoding means, and for generating a pair of control signals to said bulk PROM means and said contingency ROM storage means indicating that an access is required thereof respectively.

38. The hierarchied auxiliary memory system of claim 37 wherein said second-level decoding means further includes a second pair of programmable read-only memory means operative to receive the psuedo address set from said first pair of programmable read-only memory means for decodably generating a patch address set to said patch PROM means, and for generating a triad of control signals to said patch PROM storage means for selecting a first portion thereof, selecting a second portion thereof, and enabling thereof respectively.

39. The hierarchied auxiliary memory system of claim 38 wherein said first-level decoding means further includes gating means operative to receive the logical negation of the bulk PROM control signal, the logical positive of the contingency ROM control signal and the logical negation of the patch PROM control signal for throughputing upon concurrent receipt thereof, the contingency ROM control signal to said instruction multiplexer means for enabling thereof.

40. A contingency ROM storage module operatively coupled through a system bus to a CPUM having on-board ROM for permanent data storage of instruction code in excess of or in lieu of code in the on-board ROM comprising:

(a) Address Buffer means operative to receive addresses on the system bus from the CPUM for signal driving and correcting biasing therefor for correlative matching of signal levels;

(b) Permanent ROM storage means having addressing ranges that are transferably equivalent to ROM on board the CPUM and operative to receive driven address signals from said Address Buffer means for accessing instruction data sets mask stored therein in a plurality of partitions for transmittal on the system bus; and

(c) Instruction multiplexer means operative to receive instruction data from more than one partition of said permanent ROM storage means for selection of a instruction data set from one of the presented partitions according to a predetermined code of addresses received on the system bus from the CPUM for transmittal through the system bus to the CPUM.

41. The contingency ROM storage module of claim 40 wherein said address buffer means comprises a plurality of gating means operative to receive each of the addresses separately on the system bus for the driving thereof, and a plurality of resistive means operative to receive each of the driven addresses separately for biasing thereof.

42. The contingency ROM storage module of claim 41 wherein each of said plurality of gating means is a positive logic and gating having commonly tied inputs.

43. The contingency ROM storage module of claim 41 wherein each of said plurality of resistive means is a resistive element having a controlled potential dropped across thereof.

44. The contingency ROM storage module of claim 40 wherein said permanent ROM storage means comprises a quad of memory block means operative to receive the driven address signals for service as the memory partitions for use maximization of the limited input/output parts into the system bus for outputing a unique set of instruction data from each of said quad of memory block means.

45. The contingency ROM storage module of claim 44 wherein each of said quad of memory block means of said permanent ROM storage means include a plurality of mask programmable read-only-memory means each operative to receive a first portion of the driven addresses on the system bus at its addressing inputs and a second portion of the driven addresses or the system bus at its chip select inputs for unitary enabling thereof at any given time as accesses of instruction data onto the system bus.

46. The contingency ROM storage module of claim 44 wherein said instruction multiplexer means further includes a plurality of resistive means operative to receive each of the accessed instruction data separately on the system bus from said quad of memory block means for biasing thereof.

47. The contingency ROM storage module of claim 46 wherein each of said plurality of resistive means is a resistive element having a controlled potential dropped across thereof.

48. The contingency ROM storage module of claim 44 wherein said instruction multiplexer means further includes a pair of multiplexer block means each operative to receive a unique duality of accessed instruction data sets from said quad of memory block means for selective routing of one of the duality of accessed instruction data sets therethrough.

49. The contingency ROM storage module of claim 48 wherein each of said pair of multiplexer block means further includes a pair of multiplexer means each operative to receive one part of each of the unique duality of accessed instruction data sets for alternative selection and strobed throughputing according to a subset of the driver address signals.

50. The contingency ROM storage module of claim 40 further including address tri-state driver means operative to receive address signals in the system bus from the CPUM for output in a tri-state mode as driven signals for receipt by said address buffer means.

51. The contingency ROM storage module of claim 50 wherein said address tri-state driver means is operative to have its control line grounded for continuous operation thereof.

52. The contingency ROM storage module of claim 40 further including instruction tri-state driver means operative to receive an instruction data set from said instruction multiplexer means for output in a tri-state mode as biased driven signals on the system bus to the CPUM.

53. The contingency ROM storage module of claim 52 wherein said instruction tri-state driver means is operative to have its control line enabled by receipt of a memory read signal on the system from the CPUM for enabled operation thereof.

54. An alterable PROM storage module operatively coupled through a system bus to a central processing unit module having on-board ROM for programmable data storage of insturction code for implementation and installation of changes to the on-board ROM code comprising:

(a) Bulk PROM means operative to receive accessing addressing through the system bus from the central processing unit module for accessing instruction code programmably stored therein according to mutuality of address assigning for extensions, insertions, and large-scale overlay to code in on-board ROM;

(b) Patch PROM means operative to receive accessing addresses through the system bus from the central processing unit module for accessing instruction code programmably stored therein for single in-line bit pattern alterations through small-scale code overlay to code in on-board ROM; and

(c) address decoding means operatively coupled to receive address signals through the system bus from the central processing unit module for accessing instruction code from said bulk PROM means according to a mutuality of assigned addresses for changing on-board ROM, and for accessing instruction code from said patch PROM means as single in-line bit pattern alterations to the on-board ROM, said address decoding means further includes;

(1) first-level decoding means for partitioning said patch PROM means into a predetermined finite number of locations, and operative to receive a first portion of the address on the system bus for selecting a unique location from the set of locations through the generation of a psuedo address therefor; and

(2) second-level decoding means operative to receive the psuedo address from said first-level decoding means for pointing to a particular group as a subset of the selected location, and operative to receive a second portion of the address on the system bus for identifying a byte pointer to a multi-byte segment of the particular group.

55. The patch memory system of claim 54 wherein said second-level decoding means of said address decoding means further includes means operative to receive a third portion of the address on the system bus for pointing to a unitary byte to be selected from the multi-byte segment of the particular group for said patch PROM means.

56. The Alterable PROM storage module of claim 54 wherein said first-level decoding means of said address decoding means further includes means operative upon receipt of an address on the system bus within the effective address range of said bulk PROM means for generating a control signal representative thereof.

57. The Alterable PROM storage module of claim 56 wherein said second-level decoding means further includes means for interpreting a predetermined bit position of the byte pointer to the multi-byte segment as indicating that the effective address range of said patch PROM means is being accessed for generating a control signal representative thereof, for generating a patch address set indicating a unique instruction data set to be accessed;

and for generating a pair of control signals indicating the portion of said bulk PROM means to be accessed by the patch address set.

58. The Alterable PROM storage module of claim 56 wherein said unitary byte selection means of said second-level decoding means is further operative to hierarchically resolve conflicts as between control signal from said first and second level decoding means indicating that the requesting address overlaps effective address ranges for both said bulk and patch PROM means where the former is subordinated to the latter respectively.

59. A memory system for providing programmable extensions, insertion, and large-scale overlay to bulk code through a system bus to ROM on board a central processing unit module comprising:

(a) programmable read-only memory means operatively coupled to the system bus for storage of instruction code for transmittal upon command to the central processing unit module; and

(b) address decoding means operatively coupled to receive address signals through the system bus from the central processing unit module for accessing instruction code from said programmable read-only memory means according to a mutuality of assigned addresses for changing on-board ROM, wherein said address decoding means further includes means for specifying said programmable read-only memory means into a predetermined address range area and designating a subset of these address range areas as address effective areas, and for allowing one or more of the address effective areas to contain all or part of the instruction code.

65. The bulk memory system of claim 59 wherein said specifying means of said address decoding means further includes means for constraining the access of all the instruction code to be from one predetermined address effective area in said programmable read-only memory means.

66. The bulk memory system of claim 59 wherein said specifying means of said address decoding means further includes means for constraining access of all the instruction codes to be from more than one of the address effective areas in said programmable read-only memory means.

60. A memory system for providing programmable extensions, insertion, and large-scale overlay of bulk code through a system bus to ROM on board a central processing unit module comprising:

(a) programmable read-only memory means operatively coupled to the system bus for storage of instruction code for transmittal upon command to the central processing unit module; and

(b) address decoding means operatively coupled to receive address signals through the system bus from the central processing unit module for accessing instruction code from said programmable read-only memory means according to a mutuality of assigned addresses for changing on-board ROM, wherein said address decoding means further includes means for instituting the mutuality of assigned addresses in a mutually exclusive mode for extensions and insertions of code to on-board ROM.

63. The bulk memory system of claim 60 wherein the mutually exclusive means of said address decoding means acts to provide large-scale overlays of code to on-board ROM through branching of addresses.

61. A memory system for providing programmable extensions, insertion, and large-scale overlay of bulk code through a system bus to ROM on board a central processing unit module comprising:

(a) programmable read-only memory means operatively coupled to the system bus for storage of instruction code for transmittal upon command to the central processing unit module; and

(b) address decoding means operatively coupled to receive address signals through the system bus from the central processing unit module for accessing instruction code from said programmable read-only memory means according to a mutuality of assigned addresses for changing on-board ROM, wherein said address decoding means further includes means for instituting the mutuality of assigned addresses in a mutually inclusive mode for large-scale code overlay on-board ROM.

64. The bulk memory system of claim 61 wherein the mutually inclusive means of said address decoding means act to provide extension and insertions of code to on-board ROM through decoding of addressing.

62. A memory system for providing programmable extensions, insertion, and large-scale overlay of bulk code through a system bus to ROM on board a central processing unit module comprising:

(a) programmable read-only memory means operatively coupled to the system bus for storage of instruction code for transmittal upon command to the central processing unit module;

(b) address decoding means operatively coupled to receive address signals through the system bus from the central processing unit module for accessing instruction code from said programmable read-only memory means according to a mutuality of assigned addresses for changing on-board ROM; and

(c) patch memory means operatively coupled to the system bus for single in-line bit pattern alterations to read-only memory on-board the central processing unit module for allowing said programmable read-only memory means to be accessed through said address decoding means by addresses patched into the on-board ROM by said patch memory means.

67. A memory system for providing programmable small-scale overlay patches to a system bus read-only memory on board a central processing unit module for single-in-line-bit pattern alterations through a system bus to a central processing unit module comprising:

(a) programmable read-only memory means operatively coupled to the system bus for storage of instruction code for transmittal upon command to the central processing module; and

(b) address decoding means operatively coupled to receive address signals through the system bus from the central processing unit module for accessing instruction code from said programmable read-only memory means as single-in-line-bit pattern alterations to the on-board ROM, wherein said address decoding means further includes;

(1) first-level decoding means for partitioning the programmable read-only memory into a predetermined finite number of locations, and operative to receive a first portion of the address on the system bus for selecting a unique location from the set of locations through the generation of a psuedo address therefor; and

(2) second-level decoding means operative to receive the psuedo address from said first-level decoding means for pointing to a particular group as a subset of the selected location, and operative to receive a second portion of the address on the system bus for identifying a byte pointer to a multi-byte segment of the particular group.

68. The patch memory system of claim 67 wherein said second-level decoding means of said address decoding means further includes means operative to receive a third portion of the address on the system bus for pointing to a unitary byte to be selected from the multi-byte segment of the particular group.