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Hardware Reference Manual MCU500 Mobile Locator/Control Unit
100-00191 Revision 1.01 13
4.3 COM2 serial port
The secondary serial port (COM2) is provided on a standard DB9 male
connector, configured as a DTE with a pin-out which is compatible with an IBM
PC/AT serial port:
Pi
n
Na
m e
Description
1 DC
D Data Carrier Detect
(inpu t)
2 RX
D Re ceive Da ta (inpu t)
3 TXD Trans m it Data (outp ut)
4 DT
R Data Terminal Ready
(outp ut)
5 GN
D Ground
6 N/C No connection
7 RTS Request To Send
(outp ut)
8 CTS Clea r To Sen d (input)
9 MB
US Nokia Message Bus
(MBUS)
The secondary serial port operates at standard RS232/CCITT V.24 voltage
levels, TTL/CMOS 5V levels or inverted TTL/CMOS levels, selected by internal
jumpers. This allows the communications port to be used with a wide range of
data communications providers/devices including those with TTL/CMOS voltage
levels.
In addition to these signal levels it is possible to configure the secondary serial
port to work with the Nokia Message Bus (MBUS) protocol used on many of
Nokia’s GSM mobile phones and Tetra radios.
WARNING: due to the nature of the secondary channel’s ability to switch
between TTL/CMOS and RS232 levels it is possible to connect an RS232 device
to the MCU500 while it is configured for TTL/CMOS input/output - this may
damage the unit. Do not change the port settings fronm the factory default
(RS232) unless you are sure that the voltage levels are correct for both devices.
4.4 Auxiliary port