hanj@bronze.ucs.indiana.edu (Jining Han) (05/25/91)
I have a very standard 286 (AMI bios), with 2 parallel ports and 2 serial ports. The problem is, when I put a modem in, one of the serial ports is disabled (com1 if I set modem to use com1 or com3, com2 if I set modem to use com2 or com4). I have seen a lot of interrupt conflict problems where the modem would not work well if the switches or jumpers are not correctly set. But I have never seen any modem that disables the serial ports. Any ideas? Thanks in advance. Jining Han Indiana University PS. The modem I am using is Atrie, by Atrie Technology Inc. in Taiwan. -- --------------------------------------------------------------------- Jining Han | Indiana University ---------------------------------------------------------------------
valley@gsbsun.uchicago.edu (Doug Dougherty) (06/10/91)
hanj@bronze.ucs.indiana.edu (Jining Han) writes: >I have a very standard 286 (AMI bios), with 2 parallel ports and >2 serial ports. The problem is, when I put a modem in, one of the >serial ports is disabled (com1 if I set modem to use com1 or com3, >com2 if I set modem to use com2 or com4). You have to disable one of the on-board serial ports when you install an internal modem. Else you end up with two devices trying to be the same COM port. (I.e., I think the thing you don't realize is that the internal modem has a built-in serial port) -- (Another fine mess brought to you by valley@gsbsun.uchicago.edu)
david@kessner.denver.co.us (David Kessner) (06/11/91)
In article <1991Jun10.153842.12545@midway.uchicago.edu> valley@gsbsun.uchicago.edu (Doug Dougherty) writes: >hanj@bronze.ucs.indiana.edu (Jining Han) writes: >>I have a very standard 286 (AMI bios), with 2 parallel ports and >>2 serial ports. The problem is, when I put a modem in, one of the >>serial ports is disabled (com1 if I set modem to use com1 or com3, >>com2 if I set modem to use com2 or com4). > >You have to disable one of the on-board serial ports when you install an >internal modem. Else you end up with two devices trying to be the same >COM port. (I.e., I think the thing you don't realize is that the >internal modem has a built-in serial port) >-- > (Another fine mess brought to you by valley@gsbsun.uchicago.edu) Ahh, no. To be more precise, in the standard configurations an AT can support four serial ports (more in not-so-standard configurations). Each port has an IRQ# and an I/O port address. I forgot the I/O port addresses but that is not what we want to focus on anyway. The IRQ's are the real issue. Here are the standard IRQ#'s for the COM Ports: COM1 - IRQ4 COM2 - IRQ3 COM3 - IRQ4 COM4 - IRQ3 As you see, the odd-numbered COM ports use the same IRQ (as do the even ones). Because of the way the PC's IRQ's are designed, IRQ's cannot be shared between devices. What this means to the rest of us is that COM1 cannot be used at the same time as IRQ3 (same for IRQ2 and IRQ4). This does not mean that one COM port must be disabled-- just that it cannot be used when the other one is. Putting a mouse on COM1 makes COM3 just about useless (since a mouse is used all the time), but you could connect a modem/ printer/plotter/etc to COM2 and COM4 without any problem. -- David Kessner - david@kessner.denver.co.us | 1135 Fairfax, Denver CO 80220 (303) 377-1801 (p.m.) | Reunite PANGEA! Compuserve? Isn't that some sort of FIDO BBS? |
knudsen@cbnewsd.att.com (michael.j.knudsen) (06/14/91)
In article <1991Jun10.153842.12545@midway.uchicago.edu>, valley@gsbsun.uchicago.edu (Doug Dougherty) writes: > You have to disable one of the on-board serial ports when you install an > internal modem. Else you end up with two devices trying to be the same > COM port. (I.e., I think the thing you don't realize is that the > internal modem has a built-in serial port) Uh-oh..... I have a Compaq Portable II with just one serial port, COM1:, on its multi-function card. I'm using that for my Logitech mouse. Are you saying that if I plug in an internal modem, I'll have to disable that existing COM1: port? Or is there some way I can tell the modem to be COM2:? Or tell this to the system at bootup? Thanks, mike k -- "What America needs is A Thousand Points When Lit..." knudsen@ihlpl.att.com