[net.micro.pc] IBM AT Serial Port -- Compatability with IBM PC Serial Port

patch@nsc-pdc.UUCP (Pat Chewning) (05/15/85)

I am having trouble with my AT receiving serial data at baud rates over
1200.  I suspect that it has something to do with the incompatability of the
serial controller used on the AT vrs the PC.  Heres the set-up:

	IBM AT 
	AST ADVANTAGE! multifunction board that has the serial port.
		(Uses 16450 chip?)
	Kermit Software (Also tried-out a copy of Crosstalk with same results)
		[Both these software packages were written for PC]


Using the same physical RS232 line, I have no problem doing data transfers
at 9600 baud using a Compaq [IBM PC Clone].  

	The problem shows up at baud rates greater than 1200 (although
	occasionally at 1200 baud as well).  The characters are not wrong,
	but the problem is missing characters.  Transmitting characters
	works fine, its only on receiving that I have a problem.

		Example:

		When I log in I should get:
			4.2 BSD UNIX #1: Thu May 9 11:24:35 PDT 1985
			Login:

		Instead I get something like:
			4.2DXay24:585in:

		Some shorter messages sometimes get through OK, like the
		prompt.

The manual that came with my serial card indicates that some incompatibility
exists between the serial controller chip used in the AT and the controller
chip used on the PC.  It suggests that some software written for the PC may
not operate properly on the AT.  

Does anyone know what those differences are, and in particular, what
specific changes need to be made to Kermit [I have a source] so that it will
work on the AT?  

					Thanks in advance,

					Pat Chewning
					Mechanical Engineering
					NSC Portland Development Center
					15201 NW Greenbriar Pkwy
					Beaverton, OR 97006
					(503) 629-4458