Re: ROMs for IIgs

[Wayne Stewart <waynes@intergate.bc.ca>]

David Wilson wrote:

> The reason no one sells the ROM03 is that it only works in the 1MB IIgs
> motherboard (it is two chips) and they all came with one installed. The 256KB
> IIgs motherboard came with either a single ROM00 or ROM01 chip and can not
> be upgraded. The only ROM03 chips not in motherboards would be spare parts
> from Apple but we may have passed the period Apple keeps spares for discontinued
> IIgs computers.

I'm sort of wondering why a ROM 3 board wouldn't have a processor or ROMs on
it.

>
>
> The only problem with using 32 pin EPROMs in a //gs, even if it has 32pin
> sockets is that the pinouts of the ROMs are not quite the same as those of
> EPROMs.
>
> 1Mb/128KB  EPROM        1Mb/128KB ROM
> ----------------        -------------
> 1       Vpp                     --
> 2       A16                     --
> 3       A15             1       A15
> 4       A12             2       A12
> 5       A7              3       A7
> 6       A6              4       A6
> 7       A5              5       A5
> 8       A4              6       A4
> 9       A3              7       A3
> 10      A2              8       A2
> 11      A1              9       A1
> 12      A0              10      A0
> 13      D0              11      D0
> 14      D1              12      D1
> 15      D2              13      D2
> 16      GND             14      GND
>
> 17      D3              15      D3
> 18      D4              16      D4
> 19      D5              17      D5
> 20      D6              18      D6
> 21      D7              19      D7
> 22      /CE             20      /CE
> 23      A10             21      A10
> 24      /OE             22      A16
> 25      A11             23      A11
> 26      A9              24      A9
> 27      A8              25      A8
> 28      A13             26      A13
> 29      A14             27      A14
> 30      ---             28      VCC
> 31      /PGM                    --
> 32      VCC                     --
>
> As you can see, all the pins match up EXCEPT pin 24/22. On the Apple ROM
> it is A16 while on the EPROM it is /OE and A16 has moved to pin 2.
> If you look at the circuit diagrams in the back of the IIgs hardware
> reference manual (1st edition) the signal is even called ROMOE/A16 or something
> similar. Does the ROM03 have a jumper to relocate the A16 signal?

There don't appear to be any jumpers involved. I have a ROM 3 with 28 pin ROMs
and one with 32 pin EPROMs so I tried the 28 pin ROMS in the EPROM sockets and
there was no problems booting up.

>
>
> There may be a 28 pin 128KB EPROM (the same problem occured at the transition
> from 24 pin 2732 (4KB) to 28 pin 2764 (8KB) - Motorola had a 24 pin 68764 (8KB)
> which managed to make the /CE pin do double duty as an enable and as the VPP
> pin when programming) but I do not know its part number or manufacturer.
>
> An adapter can be constructed out of a 28 pin plug and a 32 pin socket:
>
> plug    socket
> 1..21   3..23
> 22      2       A16
> 23..27  25..29
> 28      32      VCC
>         22+24   common /OE with /CE
>         1+31+32 common VPP and /PGM with VCC (I think - check this with
>                 EPROM data sheet (271001).
>         30      leave open or connect to VCC