Help with SYM-1 BASIC

[rea5245]

I'm not using any chip yet. I trying to understand what I need to buy.

- Bob

[BillO]

It might be hard to find an 8K ROM these days. That may leave you using EPROMs. The 2764 is a 28 pin chip so would require an adapter board to fit in the SYM and it's pinout is a bit different than a 2364 (A11 and A12 are in very different places). I would suggest you consider using two 2732s (which are pretty much like the 2332) and use a jumper configuration for two 4K ROMs. However, the 2332 had an active high chip select (pin 18) and the 2764 has a active low chip select so you'd have to use the following jumpers for a 2732:

B-2 (or 3)
C-2 (or 3)
F-2 (or 3)
G-2 (or 3)
K-11 & 12
L-13 & 14

You'll also have to cut some traces on the board and re-route them since A11 is not in the same spot.

What are you trying to do, get a board going that is missing the BASIC ROMs?

[Chromatix]

The AT28C64B is an 8Kx8 EEPROM that I plan to use in my 6502 Fake Finder. It has a very similar pinout to the 2364 and 2764 ROMs, which shouldn't be surprising as it's a JEDEC standard. You should be able to make it work.

[BillO]

The pinout of the AT28C64B is very similar to the 27C64/2764 and should work as a replacement for them, but both are quite a bit different than a 2364. First, they have 4 more pins. 2nd the upper address (A11 and A12) pins are in different locations. 3rd there are different numbers of CE and OE pins. The only way to use one of these (2864 or 2764) is with an adapter board.

2364th.png (46.69 KiB) Viewed 503 times

2764th.png (55.24 KiB) Viewed 503 times

While the 4K parts (2332 & 2732) have the same number of pins and would not absolutely require an adapter board, we do have the problem of A11 being in a different place and different select options. Trace cutting and re-routing will be required.

2332th.png (46.93 KiB) Viewed 503 times

2732th.png (46.38 KiB) Viewed 503 times

[GaBuZoMeu]

BillO wrote:

Trace cutting and re-routing will be required.

No, trace cutting isn't neccessary. Pin 18, 20, and 21 of each socket are brought to the jumper section. You may need a little longer wires...

Regards,
Arne

[BillO]

GaBuZoMeu wrote:

BillO wrote:

Trace cutting and re-routing will be required.

No, trace cutting isn't neccessary. Pin 18, 20, and 21 of each socket are brought to the jumper section. You may need a little longer wires...

Regards,
Arne

Okay, just got my schematic out and a good light and a good magnifying glass, and it looks like you are indeed correct. Running longer jumpers would be a better solution for sure. You must have better eyes than me!