5 packed bit data – Varec 4000 User Manual

Page 60

Modbus Implementation

Tank Gauge Transmitter

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

ATT Response
Address

Function

code

Byte

Count

Data
MSB

Data
LSB

Error
Check

Host Request
Address

Function

Code

Start Reg
H

Start Reg
L

# of Reg
H

# of Reg
L

Error
Check

ATT Response
Address

Function

code

Byte

Count

Data
MSB

Data
LSB

Error
Check