Section 3.2 explains the design of a pair of 8-bit input/output ports for IBM PC/XT/AT and compatible computers. Figure 3.11 is the complete circuit. This appendix is a guide to building the ports. Section D.1 lists components and presents a layout. Section D.2 suggests an interfacing cable and connectors. Section D.3 gives wiring instructions.And Section D.4 outlines testing and troubleshooting. The objective is a complete presentation of one construction approach. Details such as connectors and cables are somewhat arbitrary and other schemes may be substituted.

Components and Layout

The circuit in Figure 3.11 requires the following components.

1. (1) A Vector Model 4613-1 or 4617-1 wire wrap board for the IBM PC/XT or PC-AT expansion slot.

2. (2) Four 74LS373 latch/buffers.

3. (3) Two 7425 4-input NOR IC's.

4. (4) Two 74LS04 INVERTER chips.

5. (5) One 74LS138 decoder.

6. (6) Nine IC sockets: four 20-pen, one 16-pin, and four 14-pin.

7. (7) A bag of Vector T44 wire wrap terminals.

8. (8) Six .01 μf disc capacitors.

9. (9) A wire wrap tool and an assortment of wire.

Vendors for these components are in Appendix B.

Figure D.1 suggests a layout for the circuit on a PC-AT expansion board. The view is from the components side with the rear of the computer on the right. (The regular PC board differs primarily in the absence of the second plug on the bottom left.)

Along the bottom, just above the right plug, are holes for wire wrap terminals. When inserted, the terminals allow expansion slot signals to be connected to the ports circuit.