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Two functions of this card.
SO 16 to 16 pin DIL convertor
H1 contains the footprint of the SO 16 with small holes allowing wires to connect to the pads on the main PCB.
H2 is the footprint of a 16 pin DIL. These are connected together allowing the card to be used as a convertor. The 16 pin DIL device being piggybacked on top of this card.
Connecting and Decoding the 512K/512K Flash/RAM Card
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:-
| Part No | Chip | Manufacture | Speed nS | Package | Price | |||
|---|---|---|---|---|---|---|---|---|
| Min | Typ | Max | ||||||
| 1741279 | SN74LVC1G139DCTR | Ti | <2.5 | SM8 | $ 0.69 | |||
| SN74LVC1G139DCUT | Ti / Farnell | <2.5 | VSSOP | £0.404 | ||||
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Full Data Sheet for SN74LVC1G139 2-to-4 Line Decoder & Timing
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This chip on its own provides the logic for the Z88 application.
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| Inputs | Outputs | ||
|---|---|---|---|
| B /CE | A A19 | /Y1 /CE1 FLASH | /Y0 /CE0 RAM |
| 0 | 0 | 1 | 0 |
| 0 | 1 | 0 | 1 |
| 1 | X | 1 | 1 |
Circuit Diagram using 2-to-4 Line Decoder
Updated 17/11/2016
Building the circuit on a breadboard externally
Components required
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2 MSOP-8 AND 1 VSOP to IC adaptors were obtained in addition to the 5 2-to-4 Line Decoder chips.
This circuit could now be bread-boarded and tested outside the Z88 card case.
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