4
SEL Application Guide 2020-04 Date Code 20200326
When you have set up the ports on both relays and connected the communications cable, verify the
status of the channel. Target the ROKA Relay Word bit in the SEL-421-5 and the SEL-311C-1 by
entering the TAR ROKA command, and target the ROK Relay Word bit in the SEL-321-1 by
RMByPUeMIRRORED BITS RMB Pickup
Debounce Messages
1 Number of received messages before RMBypicks
up.
RMByDOeMIRRORED BITS RMB Dropout
Debounce Messages
1 Number of received messages before RMBydrops
out.
aIf PROTO = MBGA or MBGB, the RXID and TXID settings move from Port settings to Group settings. MBA and MBB use a
seven-data bit format for data encoding. The other options are MB8A, MB8B, MBGA, and MBGB, which use an eight-data bit
format. For direct fiber applications, MBA and MBB work adequately; however, select the MB8A, MB8B, MBGA, or MBGB
protocol if additional communications interface equipment is used on the channel. See [4] for further information.
bThe SEL-311C-1, at a baud rate of 9600, sends MIRRORED BITS four times per power system cycle. Ensure the baud rate of the
SEL-311C-1 matches the baud rate of the SEL-421-5.
c
x
= A or B.
dTo maintain security during a loss of communications in a POTT scheme, you can set the default state of the permissive
receive bit (RMB1A) to 0, thus RXDFLT = XXXXXXX0. In a DCB scheme, you can set the default state of the block bit (RMB1A)
to 1, thus RXDFLT = XXXXXXX1.
e
y
= 1 to 8.
Table 3 SEL-321-1 Port 2 Settings (For Communications Between SEL-421-5 and SEL-321-1 Relays)
Setting Setting Description Setting Value Comment
PROTOCOL Communications Protocol MBaEnable MIRRORED BITS communications.
SPEED Communications Baud Rate 9600bThe SEL-321-3, -4 and the SEL-321-5 are limited
to 9600.
RTS_CTS Enable Hardware Handshaking N Not needed for relay-to-relay communications.
RBADPU MIRRORED BITS Receive Bad
Pickup
60 (default) A channel error must last 60 seconds before
RBADxcasserts.
CBADPU PPM MIRRORED BITS Channel Bad
Pickup
1000 (default) CBAD asserts if the ratio of channel downtime to
total channel time exceeds this value.
TX_ID MIRRORED BITS Transmit Identifier 1 Must match the receive identifier of the remote
relay.
RX_ID MIRRORED BITS Receive Identifier 2 Must match the transmit identifier of the remote
relay.
RXDFLT MIRRORED BITS Receive Default
Status
XXXXXXXXdThe default state in place of received data in an
error condition.
RMByPUeMIRRORED BITS RMBxPickup
Debounce Messages
1 Number of received messages before RMBypicks
up.
RMByDOeMIRRORED BITS RMBxDropout
Debounce Messages
1 Number of received messages before RMBy drops
out.
aMB uses a seven-data bit format for data encoding. The other option is MB8, which uses an eight-data bit format. For direct
fiber applications, MB works adequately; however, select the MB8 protocol setting if additional communications interface
equipment is used on the channel. See [5] for further information. In the SEL-321-0, -1, if PROTOCOL = MBG, you can set
RMB
x
from Group settings instead of Global settings.
bThe SEL-321-1, at a baud rate of 9600, sends MIRRORED BITS two times per power system cycle. Ensure the baud rate of the
SEL-321-1 matches the baud rate of the SEL-421-5.
c
x
= A or B.
dTo maintain security during a loss of communications in a POTT scheme, you can set the default state of the permissive
receive bit (RMB1A) to 0, thus RXDFLT = XXXXXXX0. In a DCB scheme, you can set the default state of the block bit (RMB1A)
to 1, thus RXDFLT = XXXXXXX1.
e
y
= 1 to 8.
Table 2 SEL-311C-1 Port 2 Settings (For Communications Between SEL-421-5 and SEL-311C-1 Relays)
(Sheet 2 of 2)
Setting Setting Description Setting Value Comment
