I have designed a cartridge that only uses I/O transfers. I have tested in many different MSXs I had access and it worked without problems in all of them. However, when I tried in an NMS8280, it did not detect the cartridge.
The busdir signal is implemented as /RD OR /CS where /CS is the decoded chip select signal: NOT (IO_ADDRESS AND IORQ). OR gate is simply made by two fast-switching diodes and a 10K pull-down resistor. Does anyone if I am missing something or there is any specific thing to do with the NMS8280?
Then, has busdir to be externally pulled-up ??
The B) circuit is quite similar to the one I used: it puts busdir LOW when the IO address is decoded. However, the BJT-based inversor pulls up the output...
