APPENDIX A:
RS232 Adapter Cables
A-2
Connection to a Modem
To connect one of the RTU RS232 Ports to a Modem, you should use the FLN6458 adapter,
which ends with the male 25-pin or 9-pin D-type connector. The port may be defined either as
a MDLC protocol port or as a User Port.
The signals that appear on the male 25-pin, or 9-pin D-type connector are according to the
RS232 standard – see the following table. In this case, the RTU serves as DTE (Data Terminal
Equipment).
RS232 Function
8-pin Connector
(on RTU)
25-pin Male
9-pin Male
Direction
TX-DATA
1
→
2
3
from RTU
RX-DATA
2
←
3
2
to RTU
RTS
6
→
4
7
from RTU
CTS
3
←
5
8
to RTU
GND
4
7
5
-
DTR
8
→
20
4
from RTU
DCD (Rec line)
5
←
8
1
to RTU
To extend the cable, you may use any extension cable with male and female D-type connectors
(connected pin-to-pin, not crossed).
Before transmitting, the RTU sends RTS=ON to the modem, and waits for CTS=ON from the
modem as a condition for transmitting.
The RTU will receive data from the modem only when DCD=ON.
When using a modem in auto-answer mode (connected to a Computer port) for remote service,
the RTU does not support RTS/CTS protocol since the port is designated to operate with a
local computer as well as with a modem.
Connection to a Radio
Note: On all of the Motorola RJ45 connector heads, the numbering of the pins is different than
the standard, as shown in the figure below. Pin 1-8 are left to right rather than right to left, as
shown below. Therefore, only original Motorola cables should be used.
