1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the Systems Programming Group of the University of Utah Computer 6.\" Science Department. 7.\" 8.\" %sccs.include.redist.man% 9.\" 10.\" @(#)dcm.4 8.1 (Berkeley) 06/09/93 11.\" 12.Dd 13.Dt DCM 4 hp300 14.Os 15.Sh NAME 16.Nm dcm 17.Nd 18.Tn HP 1998642A communications multiplexer 20.Sh SYNOPSIS 21.Cd "device dcm0 at scode? flags 0xe" 22.Sh DESCRIPTION 23The 24.Tn 98642A 25is a four port 26.Tn EIA 27.Tn RS-232C 28.Pf ( Tn CCITT 29.Tn V.28 ) 30communications 31multiplexer. The 32.Tn 98642A 33has three direct-connect ports and one port with 34full modem control. 35.Pp 36Input and output for each line may set to one of following baud rates; 3750, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 389600, 19200, 38400. 39.Pp 40.Ar Flags 41is usually specified as 0xe since 3 of the 4 ports (1-3) do not support 42modem control and should be treated as hard-wired with carrier always present. 43If port 0 does not have the need for modem control then flags can be specified 44as 45.Ql 0xf . 46.Pp 47Each port on the 48.Tn 98642A 49has a 128 byte input silo and a 16 byte output silo. 50Interrupts happen on a per character basis unless the interrupt 51rate for the card reaches 70 interrupts per second at which time the 52driver changes to a 16.7ms (60 interrupts per second) polling scheme until 53the interrupt rate drops. 54.Sh FILES 55.Bl -tag -width /dev/tty0[0-9a-f] -compact 56.It Pa /dev/tty0[0-9a-f] 57.El 58.Sh DIAGNOSTICS 59.Bl -diag 60.It dcm%d port%d: silo overflow 61Input Silo has overflowed and incoming data 62has been lost. 63.Pp 64.It dcm%d port%d: uart overflow 65The 3 character buffer in the uart has 66overflowed. 67.El 68.Sh SEE ALSO 69.Xr tty 4 70.Sh BUGS 71Total throughput per card, all ports together, is limited to 76800 bits per 72second continuous input rate. 73