Appendix E - Apple II Parallel Ports

Summary

Section 3.3 explains the design of a pair of 8-bit input/output ports for the Apple II family of computers. Figure 3.19 is the complete circuit. This appendix is a guide to building the ports. Section E.I lists components and presents a layout. Section E.2 suggests an interfacing cable and connectors. Section E.3 gives wiring instructions. And Section E.4 out lines 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 3.19 requires the following components.

1. (1) A Vector Model 4609 wire wrap board for the Apple II expansion slot.

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

3. (3) One 74LS04 INVERTER.

4. (4) One 74LS138 decoder.

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

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

7. (7) Three .01 μf disc capacitors.

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

Vendors for these components are in Appendix B.

Figure E.I suggests a layout for the circuit on the expansion board. The view is from the components side with the rear of the computer on the right. Along the bottom, just above the plug, are pads for wire wrap terminals. When inserted, the terminals allow expansion slot signals to be connected to the ports circuit. The lower row starts with 1 on the left and ends on the right at 25 (which is +5). The upper row starts on the right with 26 (which is ground) and ends on the left at 50.