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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 was the next step. 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.
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 | Drawing | mm | Price | |||||
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| Min | Typ | Max | Pad Pitch | Pad width | Length | |||||||
| 1741279 | SN74LVC1G139DCTR | Ti | <2.5 | SM8 | DCT | 0.65 | 0.3 | 4.25 | $ 0.69 | |||
| SN74LVC1G139DCUT | Ti / Farnell | <2.5 | VSSOP | DCU | 0.50 | 0.25 | 3,20 | £0.403 | ||||
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The one pixel blue line for the board size is difficult to see.
| Size of board 23.11 x x15 mm | Layout with SO 16 footprint overlaid | ||||||
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| The final layout. | Holes line up with the pads that need to be soldered | ||||||
| The 7 layers | Layout over the original PCB | ||||||
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| Here are the layers as a pdf file. Zooming in is generally helpful. | Area of the original card the board will cover. C2 needs to be removed (if fitted). | ||||||
| 3D View of Card Bottom | 3D View of Card Top | ||||||
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| 42 Actual PCBs (without screen printing) | |||||||
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| PCB fitted to 512K/512K Flash/RAM Card | Connecting PCB to 512/512K Card | ||||||
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Two additional functions of this card were considered
SO 16 to 16 pin DIL converter
A converter card using this PCB was considered as
- 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 ware connected together allowing the card to be used as a convertor. A 16 pin DIL device may be piggybacked on top of this card.
Conclusion
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This proved to be impractical solution. The holes were too small to connect to the SO16 pads. Flying wires soldered directly to the pads using the 16 pin DIL holes to connect to the PCB worked. Another method may need to be considered should this facility be needed. |