From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2005-07-24 21:56:21
On Sun, Jul 24, 2005 at 01:42:12PM -0500, Jim Brain wrote: > To all: I've heard this myth of joyports being read-only often. Is it > because the joysticks are read-only? On the plus/4, they are, if I remember correctly. On the plus/4 also CASS SENSE is read-only, again, if memory serves me right. On the VIC-20, the CASS WRITE line is shared with the joystick/keyboard. I started with the C64 and remember someone claiming that touching the keyboard or joystick while loading would cause errors. In fact, only the VIC-20 is affected, and only when saving. (If you have a C2N232, run "c2n -d" and type something on the VIC-20.) So, because the VIC-20 shares an (in principle) write-only line with an (in principle) read-only line, we can conclude that the joystick ports are not read-only. The C64 has very similar joystick port and keyboard connection. It should be obvious that the ports are bidirectional if you have a look at the schematic diagram. I think I've seen documentation (maybe in the Linux kernel) of some fancy digital joysticks that use a bidirectional bitbanging protocol. Maybe they were for the Amstrad or some less widely spread machine. Marko Message was sent through the cbm-hackers mailing list
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