Are there multiple Sharp CE-150 ROMs?

[Jeff_Birt]

While again working on disassembling the CE-158 ROM (serial interface for PC-1500), I found a section of code that looks for the presence of the CE-150 printer/cassette interface. It does this by poking a small bit of code into RAM and calling it. This is done as the CE-158 can't directly 'see' the CE-150 address space.

It surprised me that it tests for three possible values: $00, $6D, and everything else. With nothing hooked to the expansion port you will get an $FF. With the CE-158 only you get an $F7 (this is just a nonsense value as nothing at this address in CE-158). With both the CE-158 and CE-150 (or just the CE-150) you get a $D7 which is the value at that address in the CE-150 ROM.

You can't directly PEEK this address form BASIC it requires twiddling the SPU/SPV lines and disabling the interrupts. Below is a bit of code in a BASIC which will poke a machine language program into RAM, run it, and print the result out (in decimal.)
If you happen to have a PC-1500 and CE-150 would you mind running this little program and posting the results? Having a CE-158 is not required. Thanks.

100:POKE &7A26,&FD,&BE,&B8,&A5,&A2,&97,&A8,&FD
110:POKE &7A2E,&81,&AE,&7A,&33,&9A,&AA
120:CALL &7A26
130:PRINT PEEK(&7A33)
140:END

[robve]

Interesting experiment.

The value I get is 109.

- Rob

[Xorand]

(03-05-2023 03:21 AM)robve Wrote:  The value I get is 109.

That's what I get with a PC-2 and the TRS-80 Printer/Cassette interface.

[Jeff_Birt]

Thanks for checking. So far nobody has found the mystery ROM. Someone did point out that the silkscreen shown in the service manual shows two different part numbers. Don't know if this was a process change revision or code change.