DCM(4) BSD/hp300 Kernel Interfaces Manual DCM(4)NAME
dcm — HP 98642A communications multiplexer
device dcm0 at scode? flags 0xe
The 98642A is a four port EIA RS-232C (CCITT V.28) communications multi‐
plexer. The 98642A has three direct-connect ports and one port with full
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,
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 over‐
Total throughput per card, all ports together, is limited to 76800 bits
per second continuous input rate.
BSD June 9, 1993 BSD