Operation Guide P341/EN O/B11
Introduction CHAPTER 1
MiCOM P341 Page 15/22
Note: *May vary according to relay type/model
S
K
1
S
K
2
MiCOM relay
Laptop
Serial communication port
(COM 1 or COM 2)
Serial data connector
(up to 15m)
25 pin
download/monitor port
Battery
9 pin
front comms port
Figure 5: Front port connection
The relay is a Data Communication Equipment (DCE) device. Thus the pin
connections of the relay’s 9-pin front port are as follows:
Pin no. 2 Tx Transmit data
Pin no. 3 Rx Receive data
Pin no. 5 0V Zero volts common
None of the other pins are connected in the relay. The relay should be connected to
the serial port of a PC, usually called COM1 or COM2. PCs are normally Data
Terminal Equipment (DTE) devices which have a serial port pin connection as below
(if in doubt check your PC manual):
25 Way 9 Way
Pin no. 3 2 Rx Receive data
Pin no. 2 3 Tx Transmit data
Pin no. 7 5 0V Zero volts common
For successful data communication, the Tx pin on the relay must be connected to the
Rx pin on the PC, and the Rx pin on the relay must be connected to the Tx pin on the
PC, as shown in Figure 6. Therefore, providing that the PC is a DTE with pin
connections as given above, a ‘straight through’ serial connector is required, i.e. one
that connects pin 2 to pin 2, pin 3 to pin 3, and pin 5 to pin 5. Note that a common
cause of difficulty with serial data communication is connecting Tx to Tx and Rx to Rx.
This could happen if a ‘cross-over’ serial connector is used, i.e. one that connects pin
2 to pin 3, and pin 3 to pin 2, or if the PC has the same pin configuration as the
relay.
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