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16C550 UART running under Windows NT 1

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BrianG

BrianG

Military
Aug 28, 2001
357
Hi folks,

We have some ruggedised laptop computers which run a data file transfer application under Windows NT. These have unreliable performance over the RS422 serial interface port (running at 19.2k with a hard-wired link to the host device) caused by occasional lost characters. (We know the host device works fine when connected to the same application on a desktop PC)

We have seen the various Microsoft notes regarding FIFO problems with the older National 16550 and its "A" variants. We have also seen reports about devices from manufacturers other than National possibly not being 100% compatible with standard driver software.

My questions are:
1)do these known bugs relate to later C-MOS versions as used in our laptops?
2)has you experienced this sort of problem and with what manufacturers chip?

Thanks in advance
 
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I remember that some of the compatible parts power-up with some of the control lines not at the same polarity as the original part. But that does not seem to be the problem that you have.

I also remember a customer asking me to NOT use 3.3 volt RS-232 chips because they were not working reliably in their application. Your saying that the use of a desktop made the link more reliable seems to point in this direction. Voltage swing, noise. Does the RS422 converter powers itself from the RS232 signals? This might be the source of the problem. Unfortunately I did not try to verify what was behind my customer's request, as the use of a 5-volt part was easier for me. On a desktop, the RS-232 drivers arepowered from the 12 volts rails.

 
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There were a lot of problems related with the 82C55 realm not as much with the 82C51A. The 16550's were supposed to run up to 115K reliability, due to a large FIFO. There was an operating system setting that allows the user to turn on and off the FIFO. If the buffer is off then characters get lost at the higher baud rates because of system scheduling and latencies. I do not know of any problems with the 16550's. Since they are 4th generation UARTs I wouldn't expect any either. If there is a problem I would immediately and strongly suspect the operating system.

Keith Cress
Flamin Systems, Inc.-
 
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