From: peter noble To: PICLIST@MITVMA.MIT.EDU Subject: 3 (or4) serial ports Date: Monday, 26 May 1997 16:05 >I have to confess that I am puzzled about all the talk about 4 serial >ports. >If you have a modem you get a fast port built in with that. Most machines >come with two ports as standard. Some, maybe most of us, use external modems. Not too much of a problem, as simultaneous use of modem/development system isn't common. A switch can handle that... >My PIC programmer uses the parallel port. My mouse uses Com1. My modem A lot of PIC programmers use the serial port. Again, the switch box can hack this, as programming the hard code into a rom is relatively infrequent ( > 10min?) Modern mouses (mice) can use the PS/2 port found on most motherboards, BTW. Still uses an interrupt, though. >uses Com4. I have no Com3 but that is no problem. I have Com2 free for >any plug in serial devices (usually PIC based). I thought it was supposed to be a bad idea to leave 'gaps' in your com port map? >Why all the hassle about a 4th port I ask myself ???? The hassle isn't getting 4 ports onto a systerm, I/O memory space isn't *that* crowded. Its the *&^% interrupts, and their scarcity!! The cheap 4 port boards wont share ints between ports, and as for sharing off-board - forget it! A solution would be a PCI based multifunction board , as the ints on them can be level, rather than edge triggered. Why would you want so many ports active? Consider this scenario. You have an emulator on one port, the rs232 of the device being emu'ed on another, the rs232 of another device which 'talks' to the emu'ed device, but has a windowed chip in it. That's 3 ports, and they *have* to be simultaneous. If you're writing a PC level program to communicate down the rs232, it becomes even trickier, as you can't even use a dumb (XT say) terminal - you need something that can run Win95. This might seem involved, but its one of a few scenario's I'm using that need > 2 ports. On this subject, anyone know where in Oz I can get the boards that are being discussed here? MikeS