Hello,

I posted earlier about having a MIDI problem, well I have debugged enough to figure out it isn't a MIDI problem, but something else. I can't figure what it is though!

I am rewriting the OS for a piece of hardware that is using an 80C537 with a 1Mbit (27C1001) EEPROM (and external RAM, not used for my tests).

I have a binary of the manufacturer OS that I have chopped down to these few lines of assembly (which start at location X0000 in the EEPROM, jumping to X01a0):

X0000:
LJMP X01a0

X01a0:
CLR IE.7 ; disables interrupts
MOV TMOD,#21H ; sets up baud rate
MOV TH1,#0FFH
SETB TCON.6
MOV SCON,#50H
SETB 99H ; sets TI0

resend:
MOV 99H,#0F8H ;sends out MIDI byte 'F8'

jump_back:
JNB 99H,jump_back ; checks TI0
CLR 99H
LJMP resend
END

everything works as I expect (from an eeprom emulator).

But if I write this and assemble to my own binary it doesn't work (?!)

The code resides at the same memory locations as the original, and the assembly is exactly the same byte for byte as the original (I checked the bytes in the emulator monitor).

So, is there something I am missing? code banking? How can the same code not work?

Any thoughts appreciated.
Thanks
John K.