Z88 Motherboard PCB

Introduction

This document forms the basis of a collaborative project between anyone who wishes to be involved.

NOTE: The Z88 Motherboard PCB section was not completed. Please go to Articles on Modifying Motherboards

Discussion Section

Here is the section where you can discuss different topics

Object

Rather than

• build the Z88 using obsolete parts that were used in the articles below, 

• cutting tracks on the old Z88 motherboard, 

• bending chip pins out so they do not connect to the board, 

This project aims to build a PCB which has the following specification.

Specification

• 512K Flash replacing the Z88 ROM

• 1M RAM. 

• 512K allocated to Slot 0

• 512K allocated to Slot 1 - option

Advantages using a PCB.

• No track modifications need to be made to the Z88 motherboard.

• The original RAM and ROM chips are carefully un-soldered and stored until recovered again..

• They are replaced with 2 off 32 pin, low profile sockets for this PCB to plug into.

• The components used, are the same proven chips that have been used in the 512K/512K Flash/RAM Cards.

• The Flash chip AMIC  A29040CL-55F is a PLCC-32 footprint. Fitting a socket, allows the chip to be removed and reprogrammed with an EPROM programmer separately.

• Using a separate adaptor card with another PLCC-32 socket, allows the chip to be reprogrammed with an EPROM ERASER.

• No card connector problems as it is on the other side.

• The Z88 can be returned to its original state, by removing the PCB and replacing the original RAM and ROM chips back into the sockets.

Main Document

General  

This board converts the footprint of the Z88 ROM and RAM to the footprint of the new chips. To keep the PCB tracks as short as possible the replacement chips will be over the Z88 ROM area. The only signal from the ROM area is the /CE. All the other signals are obtained from the RAM side.

All data, control, and address lines will be taken directly from the header to the target chip. There are two address lines that need to be collected. A17 and A18. These are located on the Z88 near the Card connector. Thin wires are used here to connect the Z88 to a couple of pins on the PCB.

The following table illustrates this.

Signals that are not used will be ignored.

1M RAM

On the 512K/512K Flash/RAM Card, the unused 512K of RAM is ignored. With this card being able to access all the signals in the Z88, the spare 512K of RAM may be allocated to any of the other card slots, 1 2 or 3 by picking up the /CE signal of that slot.

A card, of the following types, up to 512K may be used in that slot:-

• EPROM

• ROM

• Flash

but no RAM, as that has already been allocated.

Additional Signals connected to the Z88

A SIL header will be used to connect wires for

• A17 and A18, the additional address lines not provided on the headers. These are picked up from the Slot 1 external card connector, pins xx and xx.

• /CE from Slot 1, 2, or 3 to allocate 512K of RAM to that slot.

Points noted 

On the Z88 circuit diagram, the RAM is shown on the left and the ROM is shown on the right. Physically, on the Z88, the ROM is on the left and the RAM is on the right.

Building a Prototype Board

PCB Footprint Converters

To aid construction, converters will be used for the surface mount RAM, and Flash devices.

DIL or DIP packages are easier to handle and solder connecting wires to.