Epson MFJ-1278B MULTI-MODE Hardware Modem Disconnect HEADER, J4, Pin 1 Carrier Detect Input

MFJ-1278B MULTI-MODE HARDWARE

MODEM DISCONNECT HEADER, J4

The modem disconnect header, J4, on the MFJ-1278B PC board is provided for using an external modem with the MFJ-1278B. This allows use of higher-speed modems, such as 9600 baud, or more sophisticated, higher-performance modems for OSCAR or other uses.

The following information is primarily for those who wish to interface external modems to the MFJ-1278B. Familiarity with modem and serial data channel terms is assumed. The use of the modem disconnect header, J4 requires a definite working knowledge of modems and serial data communications and associated terminology. A person without the required knowledge should not do any type of modifications in the area of the modem disconnect header, J4.

The signals used at connector J4 are at standard TTL interface levels. A TTL high, or 1, is greater than +2.4 volts but less than +5.25 volts. A TTL low, or 0, is less than 0.8 volts but greater than -0.4 volts. DO NOT connect an RS-232C level modem directly to J4!

NOTE: The modem disconnect is similar, but not identical to that used in TNC 1. Be very careful about interfacing an external modem using the same cabling you may have prepared for use with TNC 1!

For users that require pin out information on the modem disconnect header, J4, MFJ provides the following pin out infromation. The connector pin-outs are as follows.

Pin 1 Carrier Detect Input

This pin tells the SIO radio port that a valid data carrier has been detected. It should be pulled high when no carrier is detected and low when a carrier is present. This line must be implemented unless the software release notes indicate otherwise. It is normally jumpered to pin 2 when the on-board modem is used.

Pin 2 Carrier Detect Output

This pin is an output from the the on-board modem and satisfies the requirements outlined for pin 1 above. It is normally jumpered to pin 1 when the on-board modem is used.

Pin 3 SIO Special Interrupt Input

This signal is routed to the radio port DCD input pin on SIO U21. This signal is normally used during modem calibration. It may also be used for other purposes; if so, these functions will be listed in the software release notes. This pin is normally jumpered to pin 4 when the on-board modem is used.

Pin 4 SIO Special Interrupt Generator Output