12-01-2021, 07:14 PM
(12-01-2021, 05:35 PM)g67wjjk Wrote:(13-05-2020, 09:14 PM)Ernest Wrote: 2) Your original Character PROM will likely be a 2516 and if you are producing a new character EPROM yourself it will likely be a 2732, only the later boards had the jumpers available to change between the two so once again some track cutting and changing of signals to drive the new character EPROM.
This has been confusing me a little bit when reading the HW NB details.
I've got a 12MHz crystal in my Microbee 32 and the Z80 chips are suffixed A, but the character EPROM is a 2716 and not a 2516.
When I was comparing the 2716 and 2732 pinouts with the HW NB details it didn't make any sense.
Essentially the 2532/2732 has an additional address pin. It is connected to MA13 on the CRTC to enable it to switch ROM halves by the displayed CHAR memory address.
The other pin switches are to accommodate the slight EPROM control signal assignments between device types such as /CS, /OE, PGM and VPP.
Again I must stress that the replacement FONT ROM must be quick enough to operate at the increased clock speed AND some factory mask programmed FONT ROMs are not fast enough either.
Being a small company, Applied Technology could only afford to order relatively small quantities of ROMs and thus the types acquired depended upon what was available at the time. This explains the variations with ROM and RAM brands used.
