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This is the second pass at the SIMM extender. It has an 74F138 decoder/demultiplexer chip added to generate the required SIMM chip selects. It has a typical propagation delay on the order of 6-8 nsec. It is set up so the SIMM in the back slot is socket is at read address 0x20200000 and the write address is 0x20400000. This method obviates the need for a standalone programmer, and there is no new software that needs to be written, since emlilo can be used to do the flash SIMM programming. It is also cheap, costing about US$5.00 for the SIMM extender and about US$1.50 or less for the 74F138 chip. If you include the cost of the Webpal in the programmer, add another US$8.00 or so :).
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