DDCMP Framer

This is a DDCMP synchronous link framer, connected to a host with a USB interface.

Documentation

For detailed documentation, look in the doc subdirectory:

1. api.md -- programming interface for the framer.
2. kicad.md -- instructions for assembling the circuit board.
3. software.md -- how to build and load the firmware.
4. design.md -- design notes.

Connections

To use the framer, connect the micro-USB board to a USB port on the computer that will control the framer.

There are a number of choices for connecting the synchronous link to whatever device you want to use it with:

1. To use a synchronous modem or modem eliminator, connect it with a straight through DB-25 cable to the male DB-25 (marked "DTE").

2. To connect to a DDCMP device such as the DMR-11 using an RS-232 connection, connect its male DB-25 connector with a straight through DB-25 cable to the female DB-25 (marked "DCE") on the framer.

3. If you have a device such as a DMR-11 that has a line card which is meant to connect to a BC55 bulkhead panel via a 40-pin ribbon cable, but you don't have or do not want to use a bulkhead panel, connect the line unit with 40 pin ribbon cable to the 40-pin header J8 (marked "To LU"). You can use either RS-232 (with bit clock generated by the framer) or integral modem operation using this connection.

4. If you want to connect the framer to a BC55 bulkhead panel (RS-232 or integral modem), connect the BC55 with a 40-pin ribbon cable to the 40-pin header J7. Do not install termination resistors on the integral modem panel (BC55A); for details, refer to doc/kicad.md.

5. You can connect integral modem coaxial cables to BNC connectors J2 (incoming data) and J3 (outgoing data). Note that DEC specifies triax cable (two shields) but those connectors are expensive so here we just use BNC connectors, which should be fine so long as you're not operating in an extremely noisy environment. Do not install terminating resistors at the framer end, they are built in to the board.