Problems with NMS8280 and IO peripherical

By andresog

Supporter (13)

Аватар пользователя andresog

12-08-2020, 14:33

Hi all,

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?

Thank you!

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By Jipe

Paragon (1528)

Аватар пользователя Jipe

12-08-2020, 14:50

By Jipe

Paragon (1528)

Аватар пользователя Jipe

12-08-2020, 16:38

see the pdf "elektcorrect" for busdir schematics on this archive

https://msxarchive.msxinfo.net/docs/hwmodsetc/hanso/hwdoityo...

By andresog

Supporter (13)

Аватар пользователя andresog

12-08-2020, 19:10

Thank you very much, Jipe.

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...

By andresog

Supporter (13)

Аватар пользователя andresog

18-08-2020, 14:16

Solved.. finally, busdir has to be forced to high or low depending on the bus direction. Thank you Jipe for the link!