pinout chart for config sockets for MTI-1600

[Nick Sayer]

Background: I have a Sun 2/170 with an MTI-1600. The output module of this
is the same as the ones we have at school on a Sun 3/160. I presume it's
generic. According to the README in the yapt I recently installed, the MTI
is the same thing as the ALM-II, but I have no confirmation of this.

The MTI-1600 has, for each RS-232 port, a 14 pin DIP socket which allows
reconfiguration of what signals appear on the DB-25 pins. It looks like
this:

     Di    1      14    pin 2
     Do    2      13    pin 3
     HSi   3      12    pin 4
     HSo   4      11    pin 5
     RDo   5      10    pin 6
     CDb   6       9    pin 8
     CDn   7       8    pin 20

Di is data input (to the Sun) Do is data output. HSi is data handshake in.
If enabled, the sun will stop output while this line is asserted. HSo is
data handshake out, opposite of HSi. CDb is a blocking Carrier Detect. If
this is NOT asserted, input will not be passed to either minor device
(>=128 or <128).  CDn is a non-blocking CD. If this is NOT asserted, input
will not be passed to the device whose minor num is < 128, but input will
not be blocked from the high-bit minor dev. RDo is the DTR-type signal,
which lowers briefly when the file is closed.

On the right side of the connector are lines leading to the pins on the
RS-232.

In the following section, modem control refers to the DSR, DTR and DCD
lines used force modems on hook and return carrier statuses. Flow control
refers to CTS and RTS.

Here are some configurations:

To make a port a DCE with no flow control and no modem control (as for a
three-wire tty):

1-14, 2-13, 3-4, 5-7.

To make a DTE with no flow control, but modem control (as to hook up a
Hayes modem with no speed locking):

1-13, 2-14, 3-4, 5-8, 7-9.

To make a DTE with flow and modem control (as for a Telebit with speed
locking):

1-13, 2-14, 3-11, 4-12, 5-8, 7-9.

To make a DCE with flow and modem control (who knows why??):

1-14, 2-13, 3-12, 4-11, 5-10, 6-9, 7-8.

These blocks are designed to allow store-bought 9 wire RS-232 cables to do
the interconnects (1-8+20, wired straight with no crossing - same pins go
to each other on each side), with all the moving of signals from one place
to another in the blocks.  For example, there is not much use for CDb
since it will screw up echoing and result codes from modems when using the
dialout minor device node, as for uucp. It should always just be left
alone. CDn should go to the carrier indicator of the modem, or left
floating on a direct tty. If you do this, it will not be necessary to
fiddle with the kernal to set up ports for soft DCD when use with
non-modem devices. Just stick in the right kind of module for each device.
If you move a device, just swap blocks.  There is no need to even shut the
system down.

I sould note that none of this is official from Systech, and although the
acronyms for the left-hand side look weird, I made them up to insure they
are not confused with each other in a particular configuration. For
example, if you wire up a null-modem block, then really the RDo line is
DSR, not DTR as one might expect. Things like this can drive you crazy.

Nick Sayer  -  The Goose Egg public unix  -  209-952-5347 (Telebit)
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