Protocol and apparatus for a control link between a control unit and several devices

• US 5,128,666 A
• Filed: 02/20/1990
• Issued: 07/07/1992
• Est. Priority Date: 04/28/1987
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Poret, Michel, Robbe, Jean-Claude, Munier, Jean-Marie
• Primary Examiner(s): Yusko, Donald J.
• Assistant Examiner(s): Weissman, Peter
• Application Number:
  US07/573,108
• Time in Patent Office: 868 Days
• Field of Search: 340/825.05, 340/825.06, 340/825.07, 340/825.08, 340/502, 340/505, 340/825.54, 340/313, 340/314, 370/24, 370/32, 375/7, 375/8, 455/54
• US Class Current: 340/2.4
• CPC Class Codes: G06F 13/423 with synchronous protocol

Abstract

An interface and protocol for linking devices (18) with a control unit (10). The interface includes a dedicated request line (30) per device, a dot-ORed acknowledge line (32), at least one clock line (38) transmitting sets of N clock pulses from the control unit to a device during each data exchange, two data line (34, 36) for serial duplex data transmission and a pair of shift registers one being positioned in the control unit and another being positioned in each of the devices. The protocol is such that for either a read or a write operation the control unit issues two request signals in spaced relationship on the request line and the selected device responds with two acknowledge signals is spaced relationship on the acknowledge line with each one of the acknowledge signals falling after the fall of its associated request signal.

Claims

1. A control link (16) for exchanging data between a control unit (10,14) and a plurality of devices connected to said control unit, including with reference to the control unit:

an outgoing clock line (38) provided to each device, an outgoing DATA line (34), shift register means including device shift registers (44) and control unit shift register (42) respectively located within said devices and said control unit, and an ingoing DEVICE DATA line, said control link being characterized in that it includes;

an outgoing request line (30) dedicated to each device for individually selecting a given device to be written into or read from by the control unit;

an ingoing acknowledge line (32) for acknowledging the receipt by a given device of a request signal transmitted by the control unit;

in each device, a data ingoing port (DI) for receiving data from the control unit and a data outgoing port (DO) for sending data to the control unit;

in each device, means (80,76) for wrapping the data ingoing port to the data outgoing port when the device is not selected by a request signal from the control unit; and

means (78,76) for connecting the device shift register (44) of a device selected by the receipt of a request signal from the control unit into a loop (74) formed by the control unit shift register (42), the outgoing data line (34) and the ingoing device data line (36), with exchange of data between the control unit and a selected one of the plurality of devices for each write or read operation being controlled by the control unit issuing a first request signal on the request line to the selected one of the plurality of devices, with said selected one of the plurality of devices responding to said control unit with a first acknowledge signal on the ingoing acknowledge line (32) whereupon the control unit issues clock pulses on the outgoing clock line to shift data from the control unit shift register into the loop and the selected device issues a first status signal to said control unit whereupon said control unit issues a second request signal on the request line to the selected one of the plurality of devices, with said device responding with a second acknowledge signal on the ingoing acknowledge line (32) and a second status signal which is gated into the loop by clock pulses generated by the control unit.

2. A control link according to claim 1 further including means for permanent checking said loop when no transmission is currently made with a device, said means including a Device Control Adapter (DCA) remote wrap facility comprising a loop realized by DCA shift register (42), DCA Data Line and Device Data Line (36,34) and circuit arrangement coupled to the DCA shift register, said circuit arrangement intercepting data on said device data line and inverting the polarity of said data before the data is delivered to the DCA shift register.

3. The control link according to claim 2 further including a local wrap facility comprising a local loop realized by a conductor (149) interconnecting a serial output of said DCA shift register to said circuit arrangement.

4. The control link according to claim 3 wherein the circuit arrangement includes a logical OR circuit having an output coupled to the DCA shift register, a first and second logical AND circuit means coupled to the OR circuit means and two inverter circuits one of each connected to an input of the first and second logical AND circuit means.