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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.
+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:
+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.
+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.
+Anyway, the schematic:
+{{:schematics:pce_proto.png}}