NAME

dh − DH-11/DM-11 communications multiplexer

SYNOPSIS

DH0 at address 0x3fe010/017760020 vector 0xc8/0310
DM0 at address 0x3ff140/017770500 vector 0xc0/0300

DESCRIPTION

A dh-11 provides 16 communication lines; dm-11’s may be optionally paired with dh-11’s to provide modem control for the lines. 

Each line attached to the DH-11 communications multiplexer behaves as described in tty(4). Input and output for each line may independently be set to run at any of 16 speeds; see tty(4) for the encoding.

Bit i of flags may be specified for a dh to say that a line is not properly connected and that the line should be treated as hard-wired with carrier always present.  In the specification of dh0, indicating "flags 0x0004” causes line ttyh2 to be treated in this way. 

FILES

/dev/tty[hi][0-9a-f]
/dev/ttyd[0-9a-f]dialups

SEE ALSO

tty(4)

DIAGNOSTICS

dh%d: NXM.  No response from the LSI-11 bus on a dma transfer within a timeout period.  This occurs most frequently when the LSI-11 bus is heavily loaded and when devices which hog the bus (such as rk07’s) are present.  It is not serious. 

dh%d: silo overflow.  The character input silo overflowed before it could be serviced.  This can happen if a hard error occurs when the CPU is running with elevated priority, as the system will then print a message on the console with interrupts disabled.  It is not serious. 

4th Berkeley Distribution  —  1 August 1985