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schematics:nec-pwd-653 [2019/08/27 20:45] (current)
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 +===== NEC PWD-653 Socketed HuCard ======
  
 +{{  :​schematics:​pce_proto.jpg?​200| ​ }}I picked this up years ago and couldn'​t tell you for sure where it was used or by who.  It's an NEC PWD-653 HuCard, a single extra-thick PCB with two socketed 32-pin ROM chips. ​ Mine came with two 27C010 chips marked R-Type M0 and M1.
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 +Based on the way it's wired, the device maxes out at 2 Mbit, or a 2-meg ROM.  Quarter Megabyte. ​ I wanted to see if I could put larger chips on it, so I traced it all out and here's what I found:
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 +PCE line A17 is used as a chip-select. ​ A 74138 IC performs the switching. ​ One of the 74138 outputs holds the program line on the EPROMs high.
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 +The only weird things are the 4 solder bridges. ​ They'​re not straightforward on/off, but interlinked in a way that seems tantalizingly understandable. ​ Basically they control whether A16 is connected, and to what.  But it's possible to connect A16 to /OE as well, and the way it came someone went through the effort of closing one of the bridges (as indicated in the schematic) for no purpose at all, near as I can tell.
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 +Anyway, the schematic:
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 +{{:​schematics:​pce_proto.png}}
 
 schematics/nec-pwd-653.txt ยท Last modified: 2019/08/27 20:45 (external edit)
 
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