GarettCom 5843HRT User Manual page 23

Models 5843, 5844, 5843S and 5844S
RS232 or TTL
The communication logic and control software of the Master IED must be able to manage the receipt of its
echoed request. The receipt of the echo can be used in conjunction with a watchdog timer to continuously
verify loop integrity.
3
T
COM
When the potential on pin 7 is low, signals received on the R optical port are delivered to the IED and are
repeated out the T optical port to the next device in the loop. A high potential on pin 7 causes signals received
on the R optical port to be delivered to the IED only and are not repeated out the T port. It is not necessary for
a Slave to raise the potential of its pin 7 to transmit.
After an IED has completed its tasks mastering the loop, it must return its pin 7 to a low potential enabling its
repeater function, re-establishing loop continuity for the next IED that becomes loop Master.
Powering and Controlling pin 7 is ignored in all configurations except Peer-to-Peer loop operation.
Half duplex communication is available with this configuration.
When an IED is in the Slave state, it should not attempt to initiate a transmission while it is receiving a signal.
Since signals being received are also being repeated at the same time, any attempt to transmit its response
while still receiving, can corrupt both transmissions due to a data collision.
Any Link/Repeater that has its Repeat Switch in the "OFF" position and has a high potential on pin 7 will not
repeat signals received on its R optical port out of its T port. Only transmissions initiated by its IED are
transmitted out its T optical port.
ON
OFF
5 2
R
IED
FIGURE 9. Peer-to-Peer Loop Configuration
NOTE
3 5 2
T R
COM
IED
NOTE
NOTE
2-9
O N
OFF
3 5 2
T R
COM
IED
O N
O FF