8251 troubles

Date: Sun, 27 Apr 2008 08:23:09 -0700 From: dwight elvey <dkelvey at hotmail.com> I'm going to assume that you have an 8251A, not an 8251. If the latter, either sell it to a collector or have it bronzed and made into a tieclasp. There are substantial differences between the -A and non-A parts, all annoying. Glancing at your code, I'm a bit puzzled by the final initialization byte of 0x10. Why isn't this, say, 0x37? Why would you disable the receiver? 8251A commands are bit-inclusive; that is, ALL bits in the command register are interpreted independently of one another. Thus, 0x10 sent to the command register doesn't just reset the error flags, it also disables the transmitter and receiver and drops DTR and RTS. The implication is that since the command register's write-only, you have to remember the last command you sent if you want to reset the error flag. One of the minor annoyances of a few early Intel peripherals. Anent that last one--make certain that your handshake lines (RTS/CTS/DTR) are set to the proper levels--an inactive CTS will prevent the 8251A from transmitting. Hope this helps, Chuck