The decoder chip works. It replaces 1/4 of the 74139 for the Z88 design.
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| Part No | Chip | Manufacture | Speed nS | Package | Price | |||
|---|---|---|---|---|---|---|---|---|
| Min | Typ | Max | ||||||
| 1741279 | SN74LVC2G32QDCURQ1 | Ti | <2.5 | SM8 | $ 0.55 | |||
| SN74LVC1G139DCUT | Ti / Farnell | <2.5 | VSSOP | £0.404 | ||||
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- piggy backed (using the DIL connections) to Z88 Turbo card if the 16 Pin SOIC footprint is required or
- used on its own with pins, plugged into a 16 pin DIL socket on the board where the original 74xx139 was..
Headers and Sockets
| Photo | Dia hole mm | |||
|---|---|---|---|---|
| 8 way header |
| 1.00 | http://uk.farnell.com/te-connectivity-amp/826629-8/header-1row-8way/dp/3418364 | £0.596 |
| 0.90 | http://uk.farnell.com/te-connectivity-amp/215297-8/socket-vertical-1row-8way/dp/3419101 | £0.54 |
Building the circuit on a breadboard externally
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This photo needs to be replaced with one showing the Dual NAND gates.
The four signal and power lines can be seen connecting the card to the breadboard.
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| Note | ||||||||||||
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The names of the signals on the scope are not all the same as shown in the circuit.
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Printed Circuit Board
2-to-4 Line Decoder
Main points
- Small holes 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.
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Main points
- Fast low power decoder used
- Fast low power NAND gates used
- 4 Layer board used
- All fits in a 16 DIL footprint
4 Layer Board
Signal lines are used on all 4 layers.
| Power Allocation | |
|---|---|
| top copper | GND |
| inner 1 | GND |
| inner 2 | Vcc |
| bottom | GND |
Provisional Layout
To be updated when completed
The 7 layers
Here are the layers printed on A4 sheets. The board is small, zooming in is generally helpful.
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