Date Code 20011026 Communications 3-3
SEL-321/321-1 Instruction Manual
Hardware Protocol
The following hardware protocol is designed for manual and automatic communications.
1. If RTS_CTS = N, RTS will always be asserted.
2. If RTS_CTS = Y, RTS deasserts when the relay is busy (momentarily unable to accept
characters).
3. Port 3 does not support RTS_CTS hardware handshaking.
4. If RTS_CTS = Y, the relay does not send characters until the CTS input is asserted.
Alarm Conditions
The SEL-321 Relay asserts the ALARM output until self-tests pass when power is applied and at
any diagnostic test failure. In addition to these, the ALARM output pulses with the commands
and conditions shown in Table 3.1.
Table 3.1: Commands With Alarm Conditions
Command Condition
2ACCESS Entering Access Level 2 or
Three wrong password attempts
ACCESS Three wrong password attempts
BREAKER Entering Breaker Access Level or
Three wrong password attempts
COPY Copying a group into the active setting group
GROUP Changing the active setting group
PASSWORD Any password is changed
SET commands Changing the global settings, an active logic setting group, or the
active group setting
Main Board Jumpers
Installing and removing certain main board jumpers affects execution of some commands. Table
3.2 lists the jumpers you should be concerned with and their effects. See Jumper Settings in
Section 6: Installation for details.
Table 3.2: Hardware Jumpers That Affect Commands
Jumper Comment
P7: J105 Disables password protection when installed
P7: J106 Enables OPEN and CLOSE commands when installed
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