Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!mit-eddie!uw-beaver!uw-june!uw-entropy!dataio!pilchuck!toad!jgray From: jgray@toad.pilchuck.Data-IO.COM (Jerry Late Nite Gray) Newsgroups: comp.sys.ibm.pc Subject: Serial Port XON/XOFF problems Message-ID: <749@pilchuck.Data-IO.COM> Date: Mon, 9-Nov-87 12:00:17 EST Article-I.D.: pilchuck.749 Posted: Mon Nov 9 12:00:17 1987 Date-Received: Wed, 11-Nov-87 06:45:57 EST Sender: news@pilchuck.Data-IO.COM Lines: 60 Keywords: Serial, XON, XOFF, handshake Lately we have been trying to solve a problem with one of our hardware products in which we have trouble transferring data to a PC a high serial rates. We were hoping that XON/XOFF handshaking protocol would work properly with all software communication programs to allow flawless transferring of programmer data to and from the PC. PC to programmer transfers are fine, but the "upload" to the PC drops characters "occasionally". It seems that the actual baud rate, where things break down, depends on the software running on the PC as well as the clock rate and the class of PC/XT/AT (and assuming 386 machines, though this hasn't been tried yet). For example software not designed for throughput (translation: uses DOS interrupts for everything) can't handle 4800 baud. But even fairly high throughput packages (Procomm, Vterm, etc.) break down in the 9600 and 19200 baud range depending on the situation. Uploading to the screen is frequently flawless (and pointless when you think about it) though saving data to a file (especially to a floppy) causes character dropping. At first I thought this was due to our units not ceasing the transmission of data soon enough after receiving an XOFF character. After much experimenting with serial driver code, UART settups and the like I ruled this out and started analyzing the serial bus with some available equipment. Low and behold, it appears that the errors hardly ever occur with the events of XOFF transmission from the PC. It seems that in all of the cases I have tried so far that the software package on the PC just doesn't send out the XOFF character when it should to prevent overruns. So the point of this article is the basic question. Is the software/hardware performance for the serial port so bad in the PC domain that no high baud rate transfer can be guaranteed using XON/XOFF? I would be interested in other peoples experience in dealing with this problem. PLEASE Email directly to me. I will summarize and post to the net if there is sufficient interest. Incidently we have solutions that amount to "throttling" data by putting end-of-line delays as specified by the user so he can tailor his serial bandwidth to fit his processing overhead. This achieves "near" 9600 and 19200 baud rates (depending on DOS system). I have noticed that other software packages for the PC also support this mechanism for sending data to other machines. Thanks in advance, --------------- Jerrold L. Gray UUCP:{ihnp4|caip|tektronix|ucbvax}!uw-beaver!tikal!pilchuck!jgray USNAIL: 10525 Willows Road N.E. /C-46 Redmond, Wa. 98052 (206) 881 - 6444 x470 Telex: 15-2167