Copyright (c) 1990 The Regents of the University of California.
All rights reserved.

This code is derived from software contributed to Berkeley by
the Systems Programming Group of the University of Utah Computer
Science Department.

%sccs.include.redist.man%

@(#)dcm.4 5.1 (Berkeley) 06/29/90

C 7 dcm - HP 98642A communications multiplexer "device dcm0 at scode? 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.

Each line attached to the 98642A behaves as described in tty (4). Input and output for each line may set to one of following baud rates; 50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200, 38400. See tty (4) for the encoding.

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.

/dev/tty0[0-9a-f] tty(4) 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.

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