Relay-Remote Interface Specification; Command Structure - Comtech EF Data SMS-758 Installation And Operation Manual

SMS-758 Modem Protection Switch

4.3 Relay-Remote Interface Specification

This section defines the protocol and word/command structure of the relay-remote
interface.
The relay-remote input (J6) allows the user to execute a limited number of mode and
online commands (refer to Section 2.4.5 for connector location and pinout). These
commands are a series of 4-bit words.
The switch has a 4-line parallel interface with pull-up resistors (10K
open inputs are logic high, and logic low inputs can be generated by connecting to pin 25
of J6. The inputs can also be driven directly from TTL or CMOS family devices.
The M:N switch recognizes a word 100 msec after the change of state is detected on the
parallel interface. The words must be held for 200 msec, and should not be sent faster
than 500 msec, or slower than 10 second intervals.
The word can be repeated any number of times, but the switch only detects it the first
time it is sent. The following section describes the commands that can be executed.

4.3.1 Command Structure

A command to the switch consists of three or four words sent on the four parallel lines,
in Non-Return-to-Zero (NRZ) or Return-to-Zero (RZ) format.
The switch recognizes each word by changes of state at the relay-remote inputs. After
debounce, the switch identifies the word. If all words are valid and the EXECUTE word
is received, the switch performs the command.
The command words START and EXECUTE are defined in Table 4-3. Target words are
defined in Table 4-4. The six command functions are defined in Table 4-5.
A valid command structure consists of words in the following order:
1. The START word begins all messages.
2. The COMMAND word follows the start word.
3. If the command affects the online or offline status of a prime modulator or
4. The EXECUTE word follows the target (or command) word.
MN/SMS758 Rev. 3
demodulator, the next 4-bit word must be the TARGET word. The format for the
target word is the BCD number for the prime modulator or demodulator. The
target word is not sent if the backup is to be taken offline, or AUTO or
REMOTE mode is selected.
Theory of Operation
Ω
to +5V). Thus,
4–7