Campbell Scientific CR6 CR6 Measurement and Control System - Page 248

Serial I/O: Capturing Serial Data

Page 248 highlights

Section 7. Installation 7.9.16 Serial I/O: Capturing Serial Data The CR6 communicates with smart sensors that deliver measurement data through serial data protocols. Read More See Telecommunications and Data Retrieval (p. 393) for background on CR6 serial communications. 7.9.16.1 Introduction Serial denotes transmission of bits (1s and 0s) sequentially, or "serially." A byte is a packet of sequential bits. RS-232 and TTL standards use bytes containing eight bits each. Consider an instrument that transmits the byte "11001010" to the CR6. The instrument does this by translating "11001010" into a series of higher and lower voltages, which it transmits to the CR6. The CR6 receives and reconstructs these voltage levels as "11001010." Because an RS-232 or TTL standard is adhered to by both the instrument and the CR6, the byte successfully passes between them. If the byte is displayed on a terminal as it was received, it will appear as an ASCII / ANSI character or control code. Table ASCII / ANSI Equivalents (p. 248) shows a sample of ASCII / ANSI character and code equivalents. Table 48. ASCII / ANSI Equivalents Byte Received ASCII Character Displayed Decimal ASCII Code 00110010 2 50 1100010 b 98 00101011 + 43 00001101 cr 13 00000001 ☺ 1 Hex ASCII Code 32 62 2b d 1 Read More See the appendix ASCII / ANSI Table (p. 587) 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 the appendix FP2 Data Format (p. 591). 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 248

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Section 7.
Installation
7.9.16 Serial I/O: Capturing Serial Data
The CR6 communicates with smart sensors that deliver measurement data through
serial data protocols.
Read More
See
Telecommunications and Data Retrieval
(p. 393)
for background
on CR6 serial communications.
7.9.16.1 Introduction
Serial
denotes transmission of bits (1s and 0s) sequentially, or "serially."
A byte
is a packet of sequential bits.
RS-232 and TTL standards use bytes containing
eight bits each.
Consider an instrument that transmits the byte "11001010" to the
CR6.
The instrument does this by translating "11001010" into a series of higher
and lower voltages, which it transmits to the CR6.
The CR6 receives and
reconstructs these voltage levels as "11001010."
Because an RS-232 or TTL
standard is adhered to by both the instrument and the CR6, the byte successfully
passes between them.
If the byte is displayed on a terminal as it was received, it will appear as an ASCII
/ ANSI character or control code. Table
ASCII / ANSI Equivalents
(p. 248)
shows a
sample of ASCII / ANSI character and code equivalents.
Table 48.
ASCII / ANSI Equivalents
Byte
Received
ASCII
Character
Displayed
Decimal
ASCII
Code
Hex
ASCII
Code
00110010
2
50
32
1100010
b
98
62
00101011
+
43
2b
00001101
cr
13
d
00000001
1
1
Read More
See the appendix
ASCII / ANSI Table
(p. 587)
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 the appendix
FP2 Data Format
(p. 591).
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
248