3.3 DIRECT INPUT/OUTPUT COMMUNICATIONS
For the internal timing mode, the system clock is generated internally. Therefore, the timing switch selection should be
internal timing for relay 1 and loop timed for relay 2. There must be only one timing source configured.
For the looped timing mode, the system clock is derived from the received line signal. Therefore, the timing selection
should be in loop timing mode for connections to higher order systems.
The IEEE C37.94 communications module cover removal procedure is as follows:
With power to the relay off, remove the IEEE C37.94 module (type 2G, 2H, 76 or 77 module) as follows. Record the
original location of the module to help ensure that the same or replacement module is inserted into the correct slot.
Simultaneously pull the ejector/inserter clips located at the top and at the bottom of each module in order to release the
module for removal.
Remove the module cover screw.
Remove the top cover by sliding it towards the rear and then lift it upwards.
Set the timing selection switches (channel 1, channel 2) to the desired timing modes (see description above).
Replace the top cover and the cover screw.
Re-insert the IEEE C37.94 module. Take care to ensure that the correct module type is inserted into the correct slot
position. The ejector/inserter clips located at the top and at the bottom of each module must be in the disengaged posi-
tion as the module is smoothly inserted into the slot. Once the clips have cleared the raised edge of the chassis,
engage the clips simultaneously. When the clips have locked into position, the module is fully inserted.
Figure 3–41: IEEE C37.94 TIMING SELECTION SWITCH SETTING
B90 Low Impedance Bus Differential System