Browse Prior Art Database

Microprocessor to Microprocessor Communications via an 8 Bit Data Bus

IP.com Disclosure Number: IPCOM000045422D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 4 page(s) / 60K

Publishing Venue

IBM

Related People

Freeman, BJ: AUTHOR [+2]

Abstract

A mechanism is described for enabling various types of data and control information to be transferred from a first microprocessor to a second microprocessor and vice versa over an 8-bit data bus. Among other things, handshaking functions are accomplished by transferring command bytes and status bytes back and forth across the 8-bit data bus. This multiple usage of the data bus substantially reduces the total number of lines running between the two microprocessors.

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Microprocessor to Microprocessor Communications via an 8 Bit Data Bus

A mechanism is described for enabling various types of data and control information to be transferred from a first microprocessor to a second microprocessor and vice versa over an 8-bit data bus. Among other things, handshaking functions are accomplished by transferring command bytes and status bytes back and forth across the 8-bit data bus. This multiple usage of the data bus substantially reduces the total number of lines running between the two microprocessors.

This unique communication mechanism will be described for the case of the data processing system shown in Fig. 1. As there indicated, an IBM Series/1 processor is coupled by way of an I/O channel to an I/O controller card on which is located a first of the two microprocessors. This controller card is, in turn, coupled to a printer card by way of an 8-bit data bus, the second microprocessor being located on this printer card. The printer card controls the operation of a wire matrix printer (not shown). The following types of information can be transferred between the controller microprocessor and the printer card microprocessor via the 8-bit data bus: device control blocks, print data, condition codes, interrupt status bytes, interrupt information bytes, wire image data, microcode alteration data, immediate device control block (IDCB) command bytes and internal identification information.

Whenever a byte of information is transferred across the 8-bit data bus, an interrupt signal is also supplied to the receiving microprocessor. The interrupt line for the controller microprocessor is indicated in Fig. 1. The interrupt line for the printer card microprocessor is one of the lines in the 5-bit control bus. When the printer card microprocessor is interrupted with a byte of information at the input port, additional lines in the control bus indicate whether the byte of information is a command byte or, on the other hand, a byte of data.

Normally, the controller card initiates all activity on the 8-bit data bus and normally this occurs as a result of I/O commands received from the Series/1 processor. Because of this, the microprogram for the controller microprocessor is able to determine from the control information accompanying the I/O command whether the information it is receiving from the printer card is data or status information. It is, however, possible for the printer card to initiate certain functions once the 8-bit data bus is in a quiescent state. Two such functions are the "Attention Interrupt" and "Reset Busy After Reset" functions. Once initiated, these functions proceed down the normal response sequences.

Figs. 2-5 indicate various signalling sequences for different types of communications between the controller microprocessor and the printer card microprocessor. The items shown in Figs. 2-5 are various types of information bytes which are transferred via the 8-bit data bus. The arrows point to...