30 Mar
2006
30 Mar
'06
11:02 a.m.
What sort of EPROMs are used (how big, etc) ?
Two of the EPROMs are marked HN462532G and the other two are marked
2532JDL-45. I assume they are 32k bits (4k x 8)?
What else is in the unit? My investigations of the logic board
have shown
that there are a number of chip select lines brought out on the
expansion
connecotr, but there's no sane way to put 4 EPROMs directly on that
connector. I would guess at least there's a 2-4 line decoder. And
probably some transsitors to swich the Vcc to the EPROMs to save
battery
power (the HHC itself does that trick). These components may well
be SMD
on the back side of the board, BTW.
There are four M74LS08P chips on the board with the EPROMs.
There is also another circuit board mounted underneath the one with
the EPROMs that contains lots of other chips: M74LS22P, M74LS08P x 2,
HD14002BP, M74LS00P, M74LS138P, M74LS02P, MC14013B, MC14011B.
Ouch! A lot more logic than I was expecting (I was hoping it was just an
address decoder mapping the ROMs into one of the gaps in the HHC's memory
map). This would appera to be some kind of paging circuit (you've got a
couple of D-type flip-flops there that could be used to hold the selected
bank number).
That would be a good idea. In fact, I obviously have a programmer
that can handle the chips since I was able to read their contents.
Anyone know where I can get some HN462532G chips?
I _may_ have a couple, I will take a look...
-tony