Xref: utzoo comp.sys.amiga.tech:1550 sci.electronics:3644 Path: utzoo!utgpu!attcan!uunet!husc6!bloom-beacon!tut.cis.ohio-state.edu!cs.utexas.edu!bryan From: bryan@cs.utexas.edu (Bryan Bayerdorffer) Newsgroups: comp.sys.amiga.tech,sci.electronics Subject: 8520 twiddling Message-ID: <3191@cs.utexas.edu> Date: 18 Aug 88 19:04:02 GMT Sender: news@cs.utexas.edu Reply-To: bryan@cs.utexas.edu Organization: Spam Detection & Removal Squad, Austin, TX Lines: 48 Spam-Content: Negligible See, I have this strange little device, which has an even stranger single-wire half-duplex serial port on it. The port circuit looks like this: Vdd (+5V) | | R 4.7k | | Input to device <-------+ | V (diode) = | Output from device >----+-------<-> To/from outside world The specs for the port are 1 start bit, 8 data bits, 3 to 4 stop bits, with a bit time of 104 microseconds (9600 baud). Ok, so far so good, but here's the really evil part: The start bit is always generated by the strange device, regardless of the communication direction. That means, if I'm on the other end of this wire and it's my turn to send, I have to be in input mode to detect the falling edge of the start bit, switch to output mode within <104 usec, send my 8 data bits plus 3 stop bits, and switch back to input mode to await the next start bit. Sheesh. Now, loony as I am, I want to connect this thingy to the 8520-A via a couple of pins on the Amiga parallel port. My questions are: 1. How best to buffer this on the 8520 end so that nothing gets fried. E.g., can I just wire it straight in to one bit of an 8520 peripheral data register? Or maybe duplicate the above diode logic on my end and use two bits of the 8520 (I can't see how this would help)? 2. (for comp.sys.amiga.techies) Does anyone have any example code of twiddling the Amiga's 8520s? The old, first-edition RKM/hardware manual published by C-A lists only the physical addresses for the 8520's registers. While I don't see any reason for the memory map to change, I'd like my code to run on my A3000 :-) Is there a more approved way to get at these registers than to use a hardcoded address? AdvThanksance for any and all responses. ______________________________________________________________________________ /_____/_____/_____/_____/_____/_____/_____/_____/_____/_____/_____/_____/_____/ |_____|_____|_____|_____|_____|_____|_____|_____|_____|_____|_____|_____|_____| _No dark sarcasm in the classroom|_____|_____|_____|_____|_____|_____|_____|___ |____Teachers leave the kids alone__|_____|_____|_____|_bryan@cs.utexas.edu___| ___|_____|_____|_____|_____|_____|_____|{ihnp4,seismo,...}!cs.utexas.edu!bryan_ |_____|_____|_____|_____|_____|_____|_____|_____|_____|_____|_____|_____|_____|