Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 528)

Appendix C. Serial Port Pinouts
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connect the computer DTE device to the CR800 DCE device. The following table
describes RS-232 pin function with standard DCE-naming notation.
Note Pins 1, 4, 6, and 9 function differently than a standard DCE device. This is
to accommodate a connection to a modem or other DCE device via a null modem.
Table 120. CR800 RS-232 Pin-Out
PIN: pin number
O: signal out of the CR800 to a RS-232 device.
I: signal into the CR800 from a RS-232 device.
X: signal has no connection (floating).
PIN DCE Function Logger Function I/O Description
1 DCD DTR (tied to pin 6) O* Data terminal ready
2 TXD TXD O
Asynchronous data
transmit
3 RXD RXD I
Asynchronous data
receive
4 DTR N/A X* Not connected
5 GND GND GND Ground
6 DSR DTR O* Data terminal ready
7 CTS CTS I Clear to send
8 RTS RTS O Request to send
9 RI RI I* Ring
*Different pin function compared to a standard DCE device. These pins will accommodate a
connection to modem or other DCE devices via a null-modem cable.
C.2.2 Power States
The RS-232 port is powered under the following conditions: 1) when the setting
RS232Power is set or 2) when the SerialOpen() for
COMRS232 is used in the
program. These conditions leave RS-232 on with no timeout. If SerialClose() is
used after SerialOpen(), the port is powered down and left in a sleep mode
waiting for characters to come in.
Under normal operation, the port is powered down waiting for input. Upon
receiving input there is a 40-second software timeout before shutting down. The
40-second timeout is generally circumvented when communicating with
datalogger support software
(p. 76)
because it sends information as part of the
protocol that lets the CR800 know it can shut down the port.
When in sleep mode, hardware is configured to detect activity and wake up. Sleep
mode has the penalty of losing the first character of the incoming data stream.
PakBus® takes this into consideration in the "ring packets" that are preceded with
extra sync bytes at the start of the packet. SerialOpen() leaves the interface
powered-up, so no incoming bytes are lost.
When the logger has data to send via RS-232, if the data are not a response to a
received packet, such as sending a beacon, then it will power up the interface,
send the data, and return to sleep mode with no 40-second timeout.