Messages in this thread |  | | | Date | Mon, 17 Jan 2000 15:38:57 -0500 (EST) | | From | "Richard B. Johnson" <> | | Subject | Re: Serial Port voltage drops with Linux |
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On Mon, 17 Jan 2000, Jens Benecke wrote: [SNIPPED...]
> > But now we have a somewhat different problem. > > The situation is this: When we connect the hardware to the serial port, the > signal amplitude breaks down to lower than +3V (which is miniumum for the > PC to detect a "0"). With DOS, the signal amplitude varies from -10..+10 V > (approx) for 1/0 signals. With Linux, it's -10..<+3V, and that is not > enough. >
It is possible, but highly unlikely, that the UART has been left in a strange loop-back mode. In particular, the DLAB (Divisor latch access bit) ONLY must be set when the baud-rate divisor is set (on some UARTs), or the UART will be left in a strange state once DLAB is reset.
Maybe Theodore Ts'o could check. I see in the code where UART_LCR_DLAB is ORed with 'cval'. This could cause a problem.
Cheers, Dick Johnson
Penguin : Linux version 2.3.39 on an i686 machine (800.63 BogoMips).
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