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DCM(4) Device Drivers Manual (hp300) DCM(4)

dcmHP 98642A serial communications multiplexer

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.

Flags 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 ‘0xf’.

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.


dcm%d port%d: silo overflow
Input Silo has overflowed and incoming data has been lost.
dcm%d port%d: uart overflow
The 3 character buffer in the UART has overflowed.

dio(4), intro(4), tty(4)

Total throughput per card, all ports together, is limited to 76800 bits per second continuous input rate.

January 17, 2013 OpenBSD-5.3