.\"	$NetBSD: dcm.4,v 1.10 2017/02/17 22:24:46 christos Exp $
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.\" the Systems Programming Group of the University of Utah Computer
.\" Science Department.
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.\"     from: @(#)dcm.4	8.1 (Berkeley) 6/9/93
.\"
.Dd February 17, 2017
.Dt DCM 4 hp300
.Os
.Sh NAME
.Nm dcm
.Nd
.Tn HP98642A
serial communications multiplexer
.Sh SYNOPSIS
.Cd "dcm* at dio? scode ? flags 0xe"
.Sh DESCRIPTION
The
.Tn 98642A
is a four port
.Tn EIA
.Tn RS-232C
.Pf ( Tn CCITT
.Tn V.28 )
communications
multiplexer. The
.Tn 98642A
has three direct-connect ports and one port with
full modem control.
.Pp
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.
.Pp
.Ar 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
.Ql 0xf .
.Pp
Each port on the
.Tn 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.
.Sh FILES
.Bl -tag -width /dev/tty0[0-9a-f] -compact
.It Pa /dev/tty0[0-9a-f]
.El
.Sh DIAGNOSTICS
.Bl -diag
.It dcm%d port%d: silo overflow
Input Silo has overflowed and incoming data
has been lost.
.Pp
.It dcm%d port%d: uart overflow
The 3 character buffer in the UART has
overflowed.
.El
.Sh SEE ALSO
.Xr hp300/dio 4 ,
.Xr tty 4
.Sh BUGS
Total throughput per card, all ports together, is limited to 76800 bits per
second continuous input rate.