ssfels@ai.toronto.edu (Sidney Fels) (05/15/91)
I am currently trying to get my PI to talk to a speech synthesizer through the Centronics port. I have called the hot line but haven't got anything useful back from them yet. When I look at the port on a logic analyzer it appears that the SGI is sending duplicate bytes to the synthesizer. The strobe signal for these duplicate bytes is a very short glitch which suggests that the SGI is doing something wrong. My current belief about what seems to be happening is that the SGI Centronics port is not responding to the ACKNOWLEDGE signal properly. One theory I have is that the PI cannot handle the data rate requested by the synthesizer. Does anyone know of the response time of the SGI to parallel port byte requests, i.e. when the BUSY signal drops to 0 how long before data is put on the line with an accompanying strobe, assuming that my process is waiting on the write call with extra high priority? As well, how long does it take the SGI to deal with a received ACK signal? The synthesizer works perfectly when connected to an IBM PC with either the ACK connected or disconnected. When ACK is connected the timing of the handshaking is correct. If I disconnect the ACK signal the SGI hangs on the write call. If I tie ACK to BUSY it still hangs on the write. Has anyone out there used the centronics port and encountered any difficulties? Better still, anyone know what may be the problem? Is there someway to force the SGI to ignore the ACK signal and just send a byte when BUSY goes low? Any help with this will be most appreciated. Thanks, Sidney Fels University of Toronto ssfels@ai.toronto.edu (416) 978-7453 Fax: (416) 978-1455