Section 7. Installation
Read More See ASCII / ANSI Table for a complete list of ASCII / ANSI
codes and their binary and hex equivalents.
The face value of the byte, however, is not what is usually of interest. The
manufacturer of the instrument must specify what information in the byte is of
interest. For instance, two bytes may be received, one for character 2, the other for
character b. The pair of characters together, "2b", is the hexadecimal code for "+",
"+" being the information of interest. Or, perhaps, the leading bit, the MSB (Most
Significant Bit), on each of two bytes is dropped, the remaining bits combined,
and the resulting "super byte" translated from the remaining bits into a decimal
value. The variety of protocols is limited only by the number of instruments on
the market. For one in-depth example of how bits may be translated into usable
information, see FP2 Data Format
(p. 557).
Note ASCII / ANSI control character ff-form feed (binary 00001100)
causes a terminal screen to clear. This can be frustrating for a developer
who prefers to see information on a screen, rather than a blank screen.
Some third party terminal emulator programs, such as Procomm, are
useful tools in serial I/O development since they handle this and other
idiosyncrasies of serial communication.
When a standardized serial protocol is supported by the CR800, such as PakBus
or Modbus, translation of bytes is relatively easy and transparent. However, when
bytes require specialized translation, specialized code is required in the CRBasic
program, and development time can extend into several hours or days.
7.7.17.2 I/O Ports
The CR800 supports two-way serial communication with other instruments
through ports listed in table CR800 Serial Ports
(p. 280). A serial device will often
be supplied with a nine-pin D-type connector serial port. Check the manufacture's
pinout for specific information. In many cases, the standard nine-pin RS-232
scheme is used. If that is the case then the following apply:
Connect sensor RX (receive, pin 2) to a U or C terminal set up for Tx (C1, C3).
• Connect sensor TX (transmit, pin 3) to a U or C terminal set up for Rx
(C2, C4)
• Connect sensor ground (pin 5) to datalogger ground (G terminal)
Note Rx and Tx lines on nine-pin connectors are sometimes switched by
the manufacturer.
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