Astolaf.143 net.unix-wizards utcsrgv!utzoo!decvax!duke!chico!harpo!npois!houxi!ihnss!ihps3!stolaf!sft Sat Feb 20 02:19:32 1982 Re: RTS/CTS Protocol for UNIX 4.0 Actually, this applies to anyone trying to implement RTS/CTS on just about anything... Watch out for double-buffered transmitters. Just about every UART chip on the market today is double buffered. This includes the chips used in all of the DEC serial interfaces (DL, DH, DZ, etc.). Double-buffered transmitters have two registers. One is the output shift register that holds the character that the chip is currently sending. The other holds the next character to be sent. When the chip finishes sending a character, it copies the holding register into the output register and signals "ready". You now have a full character time to put the next character into the output register. So far, so good. Unfortunately, some devices that use RTS/CTS or DTR/DSR (or MIDGE/FOOP for that matter) are very particular about timing. When they signal BUSY, they want transmission to stop after the current character. BUT there's already a character in the holding register and no way to stop it from being sent. We got burned on an Epson printer that way. (See rave on Epsons in info-cpm.) The moral: check that RTS/CTS will help you first. You might be able to get things running in tough situations by enforcing a one-character-at- a-time rule in the driver, but it'll be a lot tougher. --For the original question, I b'leve there was a V7 driver supporting such protocols (subject to above limitations) on one of the distro tapes. I suspect that you could pull the necessary mods for the VAX driver out of that. Steve Tarr ihnss!ihps3!stolaf!sft ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.