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Extended Data Bus With Direction and Enable Control Features

IP.com Disclosure Number: IPCOM000041870D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Lin, HC: AUTHOR [+2]

Abstract

Contemporary personal computer systems contain a fixed number of feature card slots for I/O attachments. One way of enabling users to attach more peripherals than are permitted by the existing complement of card slots is to provide an expansion unit, analogous to a peripheral device muntiplexer/controller, with multiple additional feature card slots and adapter cards for linking any feature slot in the computer system to any slot in the expansion unit. Desirably, these adapter cards should operate to make the expansion interface transparent to both the computer system users and the DMA (Direct Memory Access) busing facilities in the computer system. An adaptation arrangement satisfying these objectives is described here. Referring to Fig.

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Extended Data Bus With Direction and Enable Control Features

Contemporary personal computer systems contain a fixed number of feature card slots for I/O attachments. One way of enabling users to attach more peripherals than are permitted by the existing complement of card slots is to provide an expansion unit, analogous to a peripheral device muntiplexer/controller, with multiple additional feature card slots and adapter cards for linking any feature slot in the computer system to any slot in the expansion unit. Desirably, these adapter cards should operate to make the expansion interface transparent to both the computer system users and the DMA (Direct Memory Access) busing facilities in the computer system. An adaptation arrangement satisfying these objectives is described here. Referring to Fig. 1, this arrangement comprises an extender card 1, a receiver card 2, and a cable 3 linking the two cards. The extender card plugs into any one of the feature card slots in the computer system 4, and the receiver card plugs into any one of the feature card slots in the (separately powered) expansion unit/board 5. The extender card contains address buffers 6 to drive address signals to the receiver card, control signal buffers 7 to drive control signals to the receiver card, octal transceivers 8 to exchange data byte signals with the receiver card, and additional buffers 9 to receive interruption requests, DMA requests and "handshaking" control signals from the receiver card. The receiver card contains address buffers 10 to receive address signals from the extender card, control signal buffers 11 to receive control signals from the extender card, octal transceivers 12 to exchange data signals with the extender card, additional buffers 13 to drive interruption and DMA requests and handshaking signals to respective buffers 9 on the extender card, and direction/enable controls 14 which exert control over the data transceivers on both cards via lines 14a and 14b. The extender card also contains a wait-state insertion circuit 15 whose function is explained later and described in detail elsewhere in the following article. The buffers and associated drivers and receivers on these cards provide an asynchronous non-overloading interface between the computer and expansion systems. The octal transceivers are selected by controls 14 for asynchronous two-way data communication between I/O channels in the computer system and expansion unit. Referring to Fig. 2, the logical design of the receiver card operates as follows to make the operations of the expansion unit transparent to computer system users: 1. Direction controls 20 provide a low state signal on DIR output 21 during CPU idle and I/O write cycles of computer system operation, and a high state DIR output during I/O read cycles of computer system operation. When DIR is low, enable output 23 is high. The inverter 29 provides the low level at 28 necessary to enable the transceiver 46 on the receiv...