5 packed bit data – Varec 4000 User Manual
Page 60

Modbus Implementation
Tank Gauge Transmitter
50
Installation and Operations Manual
9.5.4
Coded Data
Coded data represents a table look-up value. Data written to these registers must be a valid table entry. Invalid data
may cause a Configuration Error to occur. The following example shows coded data at data address 20 (0014 Hex)
representing level units. The value 2 (0002 Hex) returned from the ATT corresponds to level units = FT-IN-16TH.
•
Hexadecimal representation 0002 (decimal 2)
•
Level unit table representation: FT-IN-16TH
9.5.5
Packed Bit Data
Packed bits represent 16 individual status bits packed into one register. The status bits have been packed this way for
systems that prefer handling only register information. These bits may also be read or written individually using a bit
command. The bits within the packed registers are grouped by data or function type. The following communication
example of packed bits shows alarm status information at data address 5 (0005 Hex) returned by the ATT.
Note!
Bit #0 is ON indicating a critical low level Alarm
Host Request
Address
Function
Code
Start Reg
H
Start Reg
L
# of Reg
H
# of Reg
L
Error
Check
01
03
00
14
00
01
XX
ATT Response
Address
Function
code
Byte
Count
Data
MSB
Data
LSB
Error
Check
01
03
02
00
02
XX
Host Request
Address
Function
Code
Start Reg
H
Start Reg
L
# of Reg
H
# of Reg
L
Error
Check
01
03
00
05
00
01
XX
ATT Response
Address
Function
code
Byte
Count
Data
MSB
Data
LSB
Error
Check
01
03
02
00
01
XX