dhq.4

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)dhq.4	2.1	3/10/87
.TH dhq 4
.SH Name
dhq \- DHQ11 communications interface
.SH Syntax
.B "device dhu0 at uba? csr 0160440 flags 0x?? vector dhurint dhuxint"
.SH Description
.NXR "DHQ11 communications interface"
.NXS "dhu interface" "DHQ11 communications interface"
.NXS "dhq keyword" "DHQ11 communications interface"
A DHQ11 provides eight communication lines with modem control.
.PP
Each line attached to the DHQ11 communications multiplexer
behaves as described in
.MS tty 4 .
Input and output for each line can be set independently
to run at any of 16 speeds.
See
.MS tty 4
for the coding.
.PP
Bit
.I i
of flags can be specified for a DHQ11
to say that a line is not properly
connected and that the line should be treated as hardwired 
with carrier always present.
Thus, specifying ``flags 0x04'' in the specification of 
.PN dhu0
would cause the third line to be treated in this way.
.NT
The 
.PN dhq
driver operates under the control of the
.PN dhu 
driver.
.NE
.SH Diagnostics
.B "dhu%d %d: DMA ERROR" 
.br
The indicated channel failed to transfer DMA
data within 21.3 microseconds of the bus request being acknowledged or
there was a memory parity error.
.PP
.B "dhu%d: DIAG. FAILURE"
.br 
The DHQ11 failed the diagnostics that
run at initialization time.
.PP
.B "dhu%d: recv. fifo overflow"
.br 
The character input fifo overflowed
before it could be serviced.  This can happen if a hard error occurs
when the CPU is running with elevated priority.  Interrupts are
disabled, and the system then prints a message on the console.
.PP
.B "dhu%d: DHU HARDWARE ERROR.  TX.DMA.START failed"
.br 
The dhq failed to clear the start bit.  Normally, this is cleared to signal 
that a DMA transfer has completed.
.SH Files
.TP 15
.PN /dev/tty??
.TP
.PN /dev/ttyd?
Dialups
.SH See Also
tty(4), MAKEDEV(8)