Campbell Scientific CR23X Micrologger - Manual (Page 245)

B-1
APPENDIX B. CR23X CONTROL PORT SERIAL I/O INSTRUCTION 15
B.1 SPECIFICATIONS
FUNCTION
Send/receive full duplex serial data through the
CR23X control ports and Computer RS-232
9-pin serial port. Received serial data can be
buffered. This prevents data from being lost
from sensors that output data without hardware
of software command prompting from the
datalogger. Received data can also have
simple ASCII filters applied to locate the
beginning of the actual data set. This is
especially useful when reading data from serial
sensors such as Global Positioning System
(GPS) Receivers.
NOTE: When the CR23X RS-232 9-Pin
port is used to read serial data from a
sensor (i.e., P15 parameter 4 = 9),
connection to a PC for normal PC208W
communications is no longer available. To
re-establish PC communications on the
CR23X RS-232
9-pin port P15 parameter 4 must be set to a
value other than 9 or P15 must be removed
entirely from the program. The program
must be re-compiled with these changes to
have normal communications on the
CR23X 9-pin RS-232 port.
INPUT
Data sent by the sensor can be ASCII data
values, hexadecimal pairs in ASCII
representation, or decimal encoded binary bytes
(Section B3, Parameter 2).
OUTPUT
Output can be a preamble set of commands to
the sensor or data from the CR23X's input
locations (Section B3, Parameter 6).
BAUD RATES
Control ports (C5,C6,C7,C8 ONLY):
300, 1200, 2400, 4800
9-pin RS-232 Port on CR23X:
300, 1200, 2400, 4800, 9600, 19200, 38400,
76800
HANDSHAKE CONTROL LINES
(applies to control ports only)
REQUEST TO SEND or DATA TERMINAL
READY (RTS/DTR)
The CR23X signals the sensor that it is ready to
send or receive data. This line is always asserted
at the start of the instruction when parameter 4,
digit A is greater than zero. If no output is
specified then the line acts like RTS and remains
asserted until all input is received. If output is
specified, the line acts like DTR, asserted during
output (Section B3, Parameter 4).
CLEAR-TO-SEND (CTS)
The sensor signals the CR23X that it is ready to
receive the preamble or data (Section B3,
Parameters 3 and 9).
LOGIC LEVELS
RS-232 - Logical 1 is low voltage. RTS/DTR
asserted is high voltage.
TTL - Logical 1 is high voltage. RTS/DTR
asserted is low voltage.
PARITY AND STOP BITS
RECEIVE
- ASCII and Hexadecimal Pairs in ASCII
Representation:
1 start bit, 8 data bits, no parity,
1 stop bit 8th bit ignored
- Binary to decimal equivalent:
1 start bit, 8 data bits, no parity,
1 stop bit
TRANSMIT
1 start bit, 8 data bits, no parity, 1 stop bit
B.2 SELECTED OPERATING DETAILS
Standard RS-232 logic levels range from 3 to 25
volts and -3 to -25 volts. The 9-pin RS-232 Port
on the CR23X will support this range of logic
levels. The maximum and minimum input to
CR23X control ports is 5 and 0 volts,
respectively. Inputs exceeding these limits
may damage the CR23X. Figure B1 gives a
circuit which may be used to limit voltage levels
to 0 to 5 volts. Each input (data and
handshake) that is out of the 0 to 5 volt range
requires one of these circuits, or equivalent.