Teledyne Meridian User Manual page 154

MERIDIAN
UNIVERSAL GAS DETECTOR
CONFIGURATION & SETUP
Start Address
3.5
Char 8Bit
time
The Address field of a
message frame con-
tains two
characters (ASCII) or
eight bits (RTU). The
individual slave
devices are assigned
addresses in the
range of 1 ... 247.
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5-54
Table 5-17: MODBUS RTU Framing
Function
8Bit
The function code field
tells the addressed
slave what function to
perform. The
following functions are
supported by MOD-
BUS poll:
The Data
01 Read Coil Status
field
02 Read Input
contains
Status
the
03 Read Holding Reg-
requested
isters
or send
04 Read Input
data.
Registers
05 Write Single Coil
06 Write Single Regis-
ter
15 Write Multiple Coils
16 Write Multiple Reg-
isters
USE AND DISCLOSURE OF DATA
prohibited.
Data CRC
N * 8Bit 16Bit
Two kinds of error
checking methods (ASCII or RTU)
are used for standard MODBUS
networks. The error checking field
contents depend upon the
method that is being used.
When RTU mode is used for char-
acter framing, the error-checking
field contains a 16-bit value
implemented as two eight-bit
bytes. The error check value is the
result of a Cyclical Redundancy
Check calculation performed on
the message contents.
The CRC field is appended to the
message as the last field in the
message. When this is done, the
low-order byte of the field is
appended first, followed by the
high-order byte. The CRC high-
order byte is the last byte to be
sent in the message.
End
3.5
Char
time