Introduction
The decoder chip works. It replaces 1/4 of the 74139 for the Z88 design.
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If the decoder chip replaced 1/4 of the 74139, could 4 of them do the job?
Using 4 decoder chips
Choosing the DECODER
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chips
Looking through the data sheets for a Texas Instruments VC1 chip found the following timings and package details:-
| Part No | Chip | Manufacture/ | Speed nS | Package | Drawing | mm | Price | ||
|---|---|---|---|---|---|---|---|---|---|
| Distributor | Max | Pad Pitch | Pad Width | Length | |||||
| 1741279 | SN74LVC1G139DCTR | Ti | <2.5 | SM8 | DCT | 0.65 | 0.3 | 4.25 | $ 0.69 |
| SN74LVC1G139DCUT Decoder | Ti / Farnell | <2.5 | VSSOP | DCU | 0.5 | 0.25 | 3.20 | £0.404 | |
| 1741279 | SN74LVC2G32QDCURQ1 | Ti | <2.5 | SM8 | DCT | 0.65 | 0.3 | 4.25 | $ 0.55 |
SN74LVC2G32DCTR OR Gate | Ti / Farnell | <2.5 | SSOP-8 | DCT | 0.65 | 0.30 | 4.25 | £0.377 | |
The 2 input positive display or gates fast timesThe same decoder chip has been chosen.
Here are is the chips chip that have has been chosen:-
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| PART NUMBERPACKAGE | BODY SIZE (NOM) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SN74LVC2G32QDCURQ1 | VSSOP (8) | 2.30 mm × 2.00 mm |
Full Data Sheets for SN74LVC1G139DCT
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