2920 Float & Tape Transmitter
MODBUSAppendix A — MODBUS Implementation
156
Installation and Operations Manual
Status Bits
In the 2920 FTT implementation, status bits contain alarms, commands, and status
information. The state of a MODBUS status bit is defined as either ON (true) or OFF (false). The
ON state is represented by a “1”. The status bits may be read with function code 1 or 2. They
may be written one at a time with function code 5 or multiple bits may be written with
function code 15. An example of a read message for bits 2 through 6 as returned by the 2920
FTT is shows as follows.
Example of Status Bit Data
Start Register 0002
Number of Registers 0004
This reads Alarm Status bit 2 through 5. The response data is 03.
Bit #2: High Advisory Alarm ON
Bit #3: High Critical Alarm ON
Bit #4: Critical Low Temp OFF
Bit #5: Advisory Low Temp OFF
Exception Responses
The exception responses returned by the 2920 FTT are listed below:
Host Request
Address
Function
Code
Start Reg
H
Start Reg
L
# of Reg
H
# of Reg
L
Error
Check
01
02
00
02
00
04
C8 09
2920 FTT Response
Address
Function
Code
Byte Count
Data
Error
Check
01
02
01
03
E1 89
Exception
Response
Reason
01
Illegal Function
Message is not allowed
02
Illegal Data Address
Data address (bit or register) requested is not defined
03
Illegal Data Value
Data value being written is out of range
04
Busy
During power-up
Summary of Contents for 2920
Page 2: ......
Page 16: ...2920 Float Tape Transmitter 1 Introduction 6 Installation and Operations Manual...
Page 114: ...2920 Float Tape Transmitter 6 Bi Phase Mark 104 Installation and Operations Manual...
Page 120: ...2920 Float Tape Transmitter 7 MODBUS 110 Installation and Operations Manual...
Page 126: ...2920 Float Tape Transmitter 9 L J TankWay 116 Installation and Operations Manual...
Page 158: ...2920 Float Tape Transmitter 14 Ordering Information 148 Installation and Operations Manual...
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