Using 5 NAND Gates to prove that there is a hardware problem was very useful, but for a production run using a single chip to replace these is the next step.

Connecting to the 512K/512K Flash/RAM Card

This card is to replace the SO 16 74HC139 chip. This chip is removed (with C2) and this card connects to the SO 16 footprint.

SO 16 to 16 pin DIL convertor

A 16 way DIL connector has been included. This allows this card to be used as a SO 16 to 16 pin DIL convertor.

Choosing a Decoder chip

Looking through the data sheets for a Texas Instruments VC1 chip found the following timings:-

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Full Data Sheet for SN74LVC1G139 2-to-4 Line Decoder & Timing

Circuit Description

This chip on its own provides the logic for the Z88 application.

Circuit Description

There are 2 inputs,

• A19 - Selects either the top half of the 1M memory space for the flash chip or the bottom half for the RAM using the A input.
• /CE - Selects this chip.

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The Games play without crashing.

Oscilloscope Readings

(To be replaced by actual readings)

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Printed Circuit Board

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Main points

• Small holes 0.47 mm are drilled in the centre of the pads of H1,so that wire links may be used to connect the signals from the 512K/512K card to the PCB.
• The pads of the footprint of the SOT-23-5 have been made longer, to enable easier soldering of the small parts.
• The bottom Left Hand corner of the PCB matches the shape of the 512K/512K Card for easy alignment.

Final Layout?

The one pixel blue line for the board size is difficult to see unless viewed full size.

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This shows the area of the original card the board will cover. C2 needs to be removed (if fitted).

The 7 layers

Here are the layers as a pdf file. The board is small, zooming in is generally helpful.

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