DHV11 — serial multiplexer with DMA output

The DHV11 is DEC’s eight-line asynchronous serial multiplexer for the QBUS, the successor to the DZV11. Its receive side is a FIFO shared by all eight lines; its transmit side is DMA: the program gives a line a buffer address and a character count, and the card fetches the characters from memory and sends them on its own. It carries full modem control. QUniLator models it from the DHV11 technical manual, EK-DHV11-TM-002. Each line runs over the network: a terminal program connects to a TCP port on the board, or the line dials out, or a browser terminal carries it. It is listed as dhv11, of type dhv11_c, and ships disabled.

UNIBUS · UniBone

DEC built the DHV11 for the QBUS. The UniBone offers the same model.

What the machine sees

Registers	Eight words from 760460: CSR, RBUF (read) / TXCHAR (write), LPR, STAT, LNCTRL, TBUFFAD1, TBUFFAD2, TBUFFCT. All but CSR and RBUF act on the line CSR bits 3:0 select
Interrupts	Receive at vector 300, transmit at 304, both BR4
Receive FIFO	256 entries, each a character with its line number, or a self-test or modem status code. A character arriving at a full FIFO marks an overrun
Transmit	DMA from a 22-bit address set in TBUFFAD1 and TBUFFAD2, for the count in TBUFFCT; or one character at a time through TXCHAR. A finished transfer sets TX.ACTION in CSR with its line number, and interrupts when transmit interrupts are enabled
Line speed	Bytes cross at the speed of the network. The speed, character length and parity in the LPR are accepted and do not slow the line
Modem	STAT reports carrier, Data Set Ready and Clear To Send while a client is connected to the selected line. STAT bit 8 reads 0, which is how software tells a DHV11 from a DHU11
Master reset	CSR bit 5 runs the self-test. A program polling the CSR sees bit 5 clear after the number of reads CVDHA expects; one that does not poll sees it clear after about 2.5 seconds, or much sooner with the skip pattern. It leaves eight codes in the FIFO — six fillers and the two ROM versions
Maintenance	LNCTRL bits 7:6 select a line’s maintenance mode, local loopback among them

Using it

1. Enable dhv11. Every line listens on a TCP port of its own: line N on 4100 + N.
2. Once the guest has opened the line — raised Data Terminal Ready on it in LNCTRL, as a getty does — connect a terminal program to the board on that port, speaking Telnet: telnet <board> 4100 reaches line 0. Before that the port refuses callers; see dtr_listen, with which dropping DTR also disconnects the client.
3. Each line can be set to another port, to a host:port it dials, or to ws for a browser terminal on the board’s WebSocket /ws/serial/dhv11/<N>. The Configurations screen shows one field per line for that. A line can be changed while the device runs; only that line’s client is dropped.

A line takes one client at a time. Lines given the same port share it, so a caller reaches whichever of them is free, and a caller arriving while every line on the port is busy is refused.

Two DHV11s can run at once: dhv11 at 760460 with vector 300, and dhv11b at 760500 with vector 310, listening on ports sixteen higher.

Vector 300 is the default of three cards

dhv11, dzv11 and DL11b all start at vector 300. Enabled together, they collide; give all but one another vector.

An enable is refused when a line that is to listen at once cannot bind its port because another program holds it. A line waiting for DTR binds its port only when the guest raises DTR, so the enable does not test it.

What has been verified

• DEC’s DHV11 diagnostic CVDHA (VDHAE0, “DHV11-M FUNC TST PART 1”) runs its complete pass on a QBone with no errors: register access, the master reset and its self-test codes, the skipped self-test, transmitter enable, the level 4 interrupt and the Background Monitor Program report.

Parameters

Settings

What a configuration stores and an operator sets.

Parameter	Short	Value	Default	What it is
tcp_role0 … tcp_role7	r0 … r7	text	listen	line n TCP role: ""/listen/connect/websocket
tcp_host0 … tcp_host7	h0 … h7	text	empty	line n connect-out host
tcp_port0 … tcp_port7	p0 … p7	number	—	line n TCP port
dtr_listen	dtrl	0 or 1	1	listen on a line’s TCP port only while the guest asserts DTR

Status

What the device reports as it runs. A configuration does not store these.

Parameter	Short	Value	What it is
rx0lamp … rx7lamp	rxl0 … rxl7	0 or 1	line n receive activity
tx0lamp … tx7lamp	txl0 … txl7	0 or 1	line n transmit activity
dtr0lamp … dtr7lamp	dtl0 … dtl7	0 or 1	line n data terminal ready
rts0lamp … rts7lamp	rtl0 … rtl7	0 or 1	line n request to send
cd0lamp … cd7lamp	cdl0 … cdl7	0 or 1	line n carrier detect
dsr0lamp … dsr7lamp	dsl0 … dsl7	0 or 1	line n data set ready
cts0lamp … cts7lamp	ctl0 … ctl7	0 or 1	line n clear to send

It also carries the parameters under parameters every card on the bus has.

In detail

tcp_role0 … tcp_role7, tcp_host0 … tcp_host7, tcp_port0 … tcp_port7

Each line’s network end, line by line: tcp_roleN, tcp_hostN and tcp_portN for line N. listen accepts one client on the port, speaking Telnet with RFC 2217; connect dials host:port and dials again when the connection drops; websocket carries the line on the board’s WebSocket /ws/serial/<device>/<N>; empty leaves the line unconnected. Every line listens by default, line N of the first DHV11 on port 4100 + N, and the second DHV11 sixteen ports higher. The Configurations screen edits a line’s three as one field: a bare port listens, host:port connects, ws is the browser terminal. Lines given the same port share it: a caller reaches whichever of them is free. A line can be retuned while the device is enabled; the change drops that line’s client and leaves the others alone.

dtr_listen

A line takes a caller only while the guest holds it open. With this on, a line’s TCP port is bound while the guest asserts Data Terminal Ready on it (LNCTRL bit 9), and given up when DTR falls, which also ends a session in progress; a caller then reaches only a line the guest is ready for. Off, every line configured to listen does so from the moment the device is enabled, whatever the guest is doing with it. Takes effect at once.

rx0lamp … rx7lamp, tx0lamp … tx7lamp, dtr0lamp … dtr7lamp, rts0lamp … rts7lamp, cd0lamp … cd7lamp, dsr0lamp … dsr7lamp, cts0lamp … cts7lamp

The dashboard’s signal lamps, one set per line: receive and transmit activity, Data Terminal Ready and Request To Send as the guest drives them in LNCTRL, and carrier, Data Set Ready and Clear To Send, which all three stand while a client is connected.