Device Drivers Manual (hp300)
NAME dcm — HP 98642A serial communications multiplexer
SYNOPSIS dcm* at dio? flags 0xe
The 98642A is a four port EIA RS-232C (CCITT V.28) communications multiplexer. The 98642A has three direct-connect ports and one port with full modem control.
Input and output for each line may be set to one of the following baud rates: 50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200, 38400.
is usually specified as 0xe since 3 of the 4 ports (1-3) do not support modem control and should be treated as hard-wired with carrier always present. If port 0 does not have the need for modem control then flags can be specified as ‘
Each port on the 98642A has a 128 byte input silo and a 16 byte output silo. Interrupts happen on a per character basis unless the interrupt rate for the card reaches 70 interrupts per second at which time the driver changes to a 16.7ms (60 interrupts per second) polling scheme until the interrupt rate drops.
dcm0 port0: silo overflow
Input Silo has overflowed and incoming data has been lost.
dcm0 port0: uart overflow
The 3 character buffer in the UART has overflowed.
BUGS Total throughput per card, all ports together, is limited to 76800 bits per second continuous input rate.