dont external MODEM's have a UART

rookie1010 · 07-23-2006, 07:14 AM

Hello

I was looking at the structure of MODEM's and came across this resource

http://whatis.techtarget.com/definit...213237,00.html

according to this external MODEM's dont have UART's, what do they use instead of UARTs?

Law · 07-23-2006, 01:34 PM

If they don't then they most likely use the internal UART. The external modem uses the PC's serial ports, but an internal modem plugs right into the system bus and comes with its own UART.

If the UART chip used is "16550xx" (where "xx" can be blank or some letters), then your PC has a high speed serial port. If UART chip used says, "8250," "8550," or "6250," then you cannot reliably use a high-speed external modem on your machine.

If necessary, identify what sort of UARTs are in your system. To do this you normally need to use some sort of software diagnostic tool; the cheapest and simplest to use for this task is Microsoft Diagnostics, or MSD.

rookie1010 · 07-23-2006, 03:54 PM

thanks for the reply

my com port has a max speed of 128000, i thought that the 16550 only did 115200 bps?

do you know which standard/ body is responsible for the numbering?

Law · 07-23-2006, 08:14 PM

The 16550 UART is more suitable for high speed transmission supporting speeds greater than 115,000 bps.

I believe it's the Institute of Electrical and Electronics Engineers (IEEE), but I have not confirmed it.

07-23-2006, 07:14 AM	#1 (permalink)
rookie1010 Master Techie Join Date: Mar 2004 Posts: 2,069	dont external MODEM's have a UART Hello I was looking at the structure of MODEM's and came across this resource http://whatis.techtarget.com/definit...213237,00.html according to this external MODEM's dont have UART's, what do they use instead of UARTs?

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07-23-2006, 01:34 PM	#2 (permalink)
Law Wizard Techie Join Date: Aug 2005 Posts: 4,171	If they don't then they most likely use the internal UART. The external modem uses the PC's serial ports, but an internal modem plugs right into the system bus and comes with its own UART. If the UART chip used is "16550xx" (where "xx" can be blank or some letters), then your PC has a high speed serial port. If UART chip used says, "8250," "8550," or "6250," then you cannot reliably use a high-speed external modem on your machine. If necessary, identify what sort of UARTs are in your system. To do this you normally need to use some sort of software diagnostic tool; the cheapest and simplest to use for this task is Microsoft Diagnostics, or MSD.

07-23-2006, 03:54 PM	#3 (permalink)
rookie1010 Master Techie Join Date: Mar 2004 Posts: 2,069	thanks for the reply my com port has a max speed of 128000, i thought that the 16550 only did 115200 bps? do you know which standard/ body is responsible for the numbering?

07-23-2006, 08:14 PM	#4 (permalink)
Law Wizard Techie Join Date: Aug 2005 Posts: 4,171	The 16550 UART is more suitable for high speed transmission supporting speeds greater than 115,000 bps. I believe it's the Institute of Electrical and Electronics Engineers (IEEE), but I have not confirmed it.