Tiny url http://tinyurl.com/jdp3qqr
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The Z88 only uses one half of this dual decode chip. This circuit may be made with
- 3 inverters
- 2 NAND gates
The inverters are slower than the NAND gates, so it was decided to use 5 NAND gates using 3 of the gates as inverters.
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| 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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The Games play without crashing.
Full 74139 Version Build
Tiny url http://tinyurl.com/zf9haly
The decoder chip above works. It replaces 1/4 of the 74139 for the Z88 design.
For the full version, adding 2 OR, dual logic gates to the outputs enables the /CE signal to the 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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Building the circuit on a breadboard externally
Components required
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2 MSOP-8 IC adaptors were obtained in addition to the DUAL TWO-INPUT POSITIVE-OR GATE chips.
This circuit could now be bread-boarded and tested.
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