shc1@ukc.ac.uk (S.H.Cogheil) (01/15/90)
I am present in the process of undertaking a project, in which I need to interface a standard 6821 PIA to an Atari ST. However, as with every project, I have a problem. My problem lies in the fact that the cartridge port has no R/W line, and that the GLUE chip does not allow you to write to ROM space anyway. (Hence I cannot use the Rom3/Rom4 lines as dummy R/W lines) At the same time I see products on the market (such as Robot Arm Controllers) which use the cartridge port, and obviously find some way of getting around the above WRITE problem. If Anybody (but anybody) has had past, present or planned future experience with interfacing to the Atari, Please could you drop me some helpful hints. Yours (a little bit more that truly) Sam. p.s. Is the DMA port a viable alternative ???
adw@ukc.ac.uk (Andy Webber) (01/15/90)
In article <2706@gos.ukc.ac.uk> shc1@ukc.ac.uk (S.H.Cogheil) writes: >My problem lies in the fact that the cartridge port has no R/W line, >and that the GLUE chip does not allow you to write to ROM space anyway. >(Hence I cannot use the Rom3/Rom4 lines as dummy R/W lines) The method I have seen used (e.g. in ST Replay) involved weird usage of the READ from cartridge port. I will see if I can find any more details in the mean time consider that a hint! >Yours (a little bit more that truly) Sam. Andy.
alex@athertn.Atherton.COM (Alex Leavens) (01/17/90)
There was an article in START (like the first or second issue), which discussed a novel way of writing to the cartridge port; basically, it involved having some decode logic in the cartridge which took an address read by the user program, and turn it into an outgoing data byte. Thus, if the user program needed to _write_ a 0x5F to the cartridge, it would _read_ from address 0xXXXX05F, where 0xXXXX was in the cartridge's address space. The act of reading this address would cause an output of that value to the device on the other side of the cartridge. One problem was that there was no addressing involved; the device on the other side had to know where to stuff that byte. I don't think it would be too hard to extend the logic of the article to provide a limited addressing capability as well (if I remember, there were 7 bits unused by this scheme, so you theoretically could get 128 addresses using an extension.) |-------------------------------------------------------------------------| |--alex | alex@Atherton.COM | Caution! Falling Opinions, next 6 miles | | Now who are you gonna believe--me, or your own lyin' eyes? | |-------------------------------------------------------------------------| -- |-------------------------------------------------------------------------| |--alex | alex@atherton.com | Caution! Falling Opinions, next 6 miles | | Now who are you gonna believe--me, or your own lyin' eyes? | |-------------------------------------------------------------------------|