Thanks to many (esp. Hal Stern). The essential checklist is:

(a) have you checked /etc/ttytab to make sure the ttyh* devices are

        turned on, have gettys running, and have "local" set correctly

        so that they will ignore the h/w carrier detect?

(b) do you have the mcp* devices configured into the kernel?

(c) do /dev/ttyh* exist?

(d) make sure you understand what ttysoftcar(8) is doing!

As it turns out, I had to do one extra little bit of "magic", rm'ing

/dev/mcp* and /dev/ttyh* and re-running

        /dev/MAKEDEV mcp0

in order to actually get things running after a kernal rebuild (which

shouldn't have been necessary, I still don't understand why the rest

of this wouldn't work right until after I did that).

The important part, however, not just for ALM-2 (aka MCP) boards, but

for ALL serial lines, is to understand something about how ttysoftcar(8)

works. I'm still not sure I do, but here's what I think I know:

In general under SunOS4.1.1 it's not necessary to fiddle with kernal

rebuilds or even eeprom settings in order to turn on or turn off

carrier detect. What IS necessary is to properly declare the ports

in /etc/ttytab. If "local" is there, software carrier detection

is turned ON (and hardware carrier detection disabled). If the

entry reads anything else, software carrier detection is turned

OFF, all of that via "/usr/etc/ttysoftcar -a > /dev/null 2>&1"

command in /etc/rc.local.

If the device is not listed in /etc/ttytab, apparently it defaults

to the flags value in the kernal configuration and/or eeprom setup.

Having said all of that, I should also add that--under some conditions

still not completely clear to me--ttysoftcar may not always work.

In particular, in using it directly (e.g., ttysoftcar [-y|-n] /dev/ttymumble)

the command sometimes seems to hang. Also, having "remote" instead

of "local" does not always seem to keep software carrier detection

off. On several systems here with modems (e.g., on ttya), I've

found myself having to add:

/usr/etc/ttysoftcar -n /dev/ttya

..at the end of /etc/rc.local in order to actually get hardware

carrier detect.