QAA@psuvm.BITNET (09/04/85)
I was in touch with a company who sells a communication program
for the IBM-PC and has a capability of communicating at 19.2K bps.
Most serial cards for the IBM-PC that I know of are only pro-
grammable to 9600 bps (according to documentation). The company
mentioned that the standard (IBM) serial port could be configured
to rates of 19.2K bps, and even as far as 38.4K bps.
Anybody know if this is possible? Is it a hardware modification
on the port, or undocumented software change?
Thanks in advance for any information!
- Tim Bieling
System Manager - ComCAD Lab - Dept of Arch. (PSUARCH)
Bitnet: Qaa @ Psuvm/Psuarch
Bieling @ Psuarch
Manager @ Psuarch
slerner@sesame.UUCP (Simcha-Yitzchak Lerner) (09/04/85)
(Original posting follows) Yes, it is possible to get a standard pc's serial card to go up to 38.4 Kbps without any hardware modifications. Most programs do not go beyond 9600 bps due to the fact that the pc's processor is too slow to process incoming data at that rate! (There are exceptions, eg:Pro-Yam will run at 38.4 Kbps - it is largly a matter of how much overhead is in the interrupt service routines. It doesn't take too much overhead before the I/O rate is outpacing the processor, thereby loosing characters). > I was in touch with a company who sells a communication program > for the IBM-PC and has a capability of communicating at 19.2K bps. > Most serial cards for the IBM-PC that I know of are only pro- > grammable to 9600 bps (according to documentation). The company > mentioned that the standard (IBM) serial port could be configured > to rates of 19.2K bps, and even as far as 38.4K bps. > > Anybody know if this is possible? Is it a hardware modification > on the port, or undocumented software change? > > Thanks in advance for any information! > > - Tim Bieling > -- Opinions expressed are public domain, and do not belong to Lotus Development Corp. ---------------------------------------------------------------- Simcha-Yitzchak Lerner {genrad|ihnp4|ima}!wjh12!talcott!sesame!slerner {cbosgd|harvard}!talcott!sesame!slerner slerner%sesame@harvard.ARPA
digger@zps.UUCP (Scott A. Miles) (09/06/85)
Yes it is possible to configure the serial port to at least 19.2K. Instead of using the dos or bios call you simply program the 8250 registers on the serial card yourself. It does work fairly well at 19.2K. I have used it to interface between AT's and digitizing tablets. Scott
bc@cyb-eng.UUCP (Bill Crews) (09/06/85)
> Yes, it is possible to get a standard pc's serial card to go up > to 38.4 Kbps without any hardware modifications. Most programs do > not go beyond 9600 bps due to the fact that the pc's processor is > too slow to process incoming data at that rate! (There are exceptions, > eg:Pro-Yam will run at 38.4 Kbps - it is largly a matter of how much > overhead is in the interrupt service routines. It doesn't take too > much overhead before the I/O rate is outpacing the processor, thereby > loosing characters). Don't forget either that other software that you may be using might turn interrupts off for periods of time that are unacceptable at those data rates. If the communications package is designed to do this while only that package is running, then fine. But under Topview or a serial network, even 9.6Kbps may not be reliably achievable. -- / \ Bill Crews ( bc ) Cyb Systems, Inc \__/ Austin, Texas [ gatech | ihnp4 | nbires | seismo | ucbvax ] ! ut-sally ! cyb-eng ! bc
hamilton@uiucuxc.Uiuc.ARPA (09/10/85)
> I was in touch with a company who sells a communication program > for the IBM-PC and has a capability of communicating at 19.2K bps. > Most serial cards for the IBM-PC that I know of are only pro- > grammable to 9600 bps (according to documentation). The company > mentioned that the standard (IBM) serial port could be configured > to rates of 19.2K bps, and even as far as 38.4K bps. > > Anybody know if this is possible? Is it a hardware modification > on the port, or undocumented software change? the hardware doesn't limit you to 9600; the ROM BIOS does. if you check out the BIOS serial port services (INT 14), you'll see that you specify the desired baud rate, parity, and framing in a single byte; the baud rate gets 3 of the 8 bits. the actual baud rate the hardware uses comes from dividing the clock frequency (1.19Mhz?) by a 16-bit number. the BIOS has a table of 8 of these divisor values, and sets the serial port baud rate by loading one of them into the UART's divisor latch. the BIOS writers chose to supply divisors for 110, 150(!), 300, 600(?), 1200, 2400, 4800, and 9600 baud. anyhow, it's a simple matter to load your own divisor with a few i/o instructions. as i recall, the divisor for 9600 is 12, 19.2K would be 6, and 38.4K would be 3.
langet@ecn-pc.UUCP (Timothy Lange) (09/10/85)
From what I understand the hardware can be driven to much faster
speeds, for example, a software based LAN that uses the serial
ports and twisted pair can run at speeds around 115K bps for
cable lengths less than 50 feet. Errors do occur but the LAN
software is suppose to detect and resend bad packets. The review
for this particular LAN said that speed must drop for greater
distances, with the lowest speed 19.2K bps for lengths around
1000 feet.
I looked up the review, it is LANLink, it said the UART can
handle 38K bps with no problem, but can go to 115.2K bps with an
occasional error. With error correcting protocol, an error now
and then can be tolerated. The review was in the August, 1985
issue of Business Computer Systems.
--
Tim Lange Engineering Business Offices
317-494-5338 Rm 120 Engineering Administration Bldg.
Purdue University West Lafayette, IN 47907
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