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Adding A Narrow ROM To the 1802 Olduino – II

June 21, 2017

Electrically this was not too bad.  I had actually picked a bad spot to cut the A14 trace but no big deal. The ROM’s A14 on pin 27 is jumpered to the RAM’s pin 1 and the ROM’s VPP on pin 1 is jumpered to VCC on its own pin 28.


Mechanically it is quite a bit trickier. I am using these little tiny pin sockets so I can remove the ROM for programming.  Even so, it barely fits under the RAM although there’s lots of room above it.  Getting the rom and sockets in place to solder was very finicky.  You normally put the pins on the IC then insert in the board and solder but these ROM chips have been through the wars and getting everything aligned was brutal.  I ended up starting with just a couple of pins at each end and inserting the chip from the back of the board where I had better access. Then I’d remove it and try it in the correct orientation.  Gradually, with a lot of fiddling I added pins, went front and back, and eventually everything lined up.

17-06-21 plenty of roomThe final mechanical issue is that there isn’t really room under the RAM for the bulky ROM chip. The RAM is just barely in its socket and it wouldn’t be reliable. I’ll have to either replace the RAM socket with something higher or use another layer of the socket pins.


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