11451 Belcher Road South, Largo FL 33773 • USA • Tel +1 (727) 447-6140 • Fax +1 (727) 442-5699 • [email protected]
F-1500 Turbine Flow Meter Manual 02/18 - 1018-6 / 35726
Page 62
Control Register Definitions
The only writable registers in this implementation are the Reset Exception Status, Reset
Meter and Reset Totalizer functions, which are implemented as ”coils” which may be
written with the Write Single Coil command (function code 05) to address 8 through 10,
respectively (register #00009 through #00011). The value sent with this command must be
either 0x0000 or 0xff00, or the meter will respond with an error message. The totalizer will
be reset or exception status cleared only with a value of 0xff00.
Error Responses
If an error is detected in the message received by the unit, the function code in the response
is the received function code with the most significant bit set, and the data field will contain
the exception code byte as follows:
Exception Code
Description
01
Invalid function code — function code not supported by device
02
Invalid data address — address defined by the start address and number of
registers is out of range
03
Invalid data value — number of registers = 0 or >125 or incorrect data with
the Write Single Coil command
If the first byte of a message is not equal to the unit’s Modbus address, if the unit detects a
parity error in any character in the received message (with even or odd parity enabled), or if
the message CRC is incorrect, the unit will not respond.
Command Message Format
The start address is equal to the desired first register number minus one. The addresses
derived from the start address and the number of registers must all be mapped to valid
defined registers, or an invalid data address exception will occur.
Device Address
8 bits, 1...247
Function Code
8 bits
Start Address
16 bits, 0...9998
N=Number of Registers
16 bits, 1...125
CRC
16 bits
Normal Response Message Format
Device Address
8 bits, 1...247
Function Code
8 bits
Byte Count =
2
x N
Data
(N) 16-bit registers
CRC
16 bits
Exception Response Message Format
Device Address
8 bits, 1...247
Function Code
8 bits
Exception Code
8 bits
CRC
16 bits
Examples
Read the exception status byte from the device with address 1:
01 07 41 E2
01 Device address
07 Function code, 04 = read exception status
A typical response from the device is as follows:
01 07 03 62 31
01 Device address
07 Function code
03 Exception status byte
62 31 CRC