Campbell Scientific CR23X Micrologger - Manual (Page 251)

APPENDIX B. CONTROL PORT SERIAL I/O INSTRUCTION 15
B-7
(A = 1 and 2 or 3 and 4). The starting control
port used for the serial output and serial input
pairs is specified as the second digit (B = 5 and
6 or 7 and 8). Control ports 2 and 3 (RTS/CTS)
and 6 and 7 (TX/RX) pairs can also be used but
this limits the repetitions to 1. RTS output in
this example, when asserted (5V), tells the
sensor that the CR23X is ready to receive
characters. The CR23X will not transmit
characters unless it sees the CTS input line
high (5V). A total of 4 control ports are being
used per repetition. A maximum of 2 repetitions
can be used in this configuration.
B.5 RS-232 SERIAL DATA
CONFIGURATION AND DATA
BUFFERING
B.5.1 DATA INPUT VIA RS-232 9-PIN
CONNECTOR
Serial data can be received through the CR23X
9-pin RS-232 port rather than through control
ports C5 - C8 if you select for parameter 4 the
single-digit option code of “9”. The advantages
of using the RS-232 port:
a. you can read in higher baud rate data
streams from 9600 to 76800 baud (300 to
4800 also supported)
b. it allows RS-232 level sensors to be
connected to the port without additional
clamping circuitry
c. it provides optical isolation which can
improve data integrity probability (P15
contains no error checking algorithms).
The RS-232 port is configured as a Data
Communications Equipment (DCE) device. The
original intention of this port was to provide
direct connection to a PC serial port which is
normally a Data Terminal Device or DTE. Since
most serial sensors are also configured as a
DCE device a null modem interface will be
required. This can be accomplished through a
simple cable as shown below or purchased
from a local computer store.
Null Modem Connection Example
9-pin D to 9 pin D
SIGNAL PIN No. PIN No.
RXD 2 to 3
TXD 3 to 2
DTR 4 to 6
GND 5 to 5
DTR 6 to 4
RTS 7 to 8
CTS 8 to 7
25 pin D to 9 pin D
SIGNAL 25 PIN No. 9 PIN No. GND (SG) - Ground (Signal GND)
TXD 2 to RXD 2 TXD - Transmit Data
RXD 3 to TXD 3 RXD - Receive Data
RTS 4 to CTS 8 RTS - Request to send
CTS 5 to RTS 7 CTS - Clear to send
DSR 6 to DTR 4 DSR - Data Send Ready
SG 7 to SG 5 DCD - Carrier Detect
DTR 20 to DSR 6 DTR - Data Terminal Ready
Null Modem Signal Connections
Connector 1 to Connector 2