Common Modbus Item Conversion

/

Append a '/' to the register or excstatus items followed by a bit number (starting at zero (0)) to access a single bit of a multi-bit data type.

.

A bit-width can be specified by appending a '.' followed by a number after the bit number specifier ('/').

B

Append a 'B' to the register to access the data as a True or False value. If the register contains a zero (0), the item value will be a zero (0).If the register contains a non-zero value, the item value will be a one (1).

B/0.n

Append a 'B' to a coil or input address, in conjunction with the '/' and '.' flags, to access consecutive addresses as an integer value. Starting conversion bit specified must be zero.
Example: 1001B/0.2 -- Access coils 1001 and 1002, combining the bit pattern into an integer.

C

Append a 'C' to the register to access the data as a single 8-bit character.

H

Append an ‘H’ to the register to access the data as a BCD value.

I

Append an 'I' to the register to access the data as a single 16-bit integer value.

L

Append an 'L' to the register to access the data as a single 32-bit integer value.

S

Append an 'S' to any of the above conversion flags (except 'B' and '/') to indicate the value is signed. Otherwise, all values will be treated as unsigned.

F

Append an ' F' to the register to access the data as a single 32-bit floating point value.

D

Append a 'D' to the register to access the data as a single 64-bit floating point value.

M

Append an 'M' to the register to access the data as a string (message).This must also be followed by a length specification in the form '[n]' where n is the number of characters in the string.

M1

Append an ‘M1’ to the register to access the data as a string (message).This is similar to the ‘M’ conversion flag, but the ‘M1’ conversion can be used to get a single character from a 16-bit register.

P

Append a 'P' to the register to access the data as a single 16-bit half-precision floating point value. The data is converted and provided to the client as 32-bit floating point. This conversion flag is not valid to use with 32 or 64 bit registers.

T

Append a 'T' to the register to convert the value read from a Julian date/time (seconds since Jan. 1, 1970) to a string. This implies that the register value that is read from the device is a Julian date/time stamp.

-

Append a '-' to the register to reverse the word and byte order specified in the register range properties. This applies only to the item with the '-'.

^

Append a '^' and a byte order code number to the register to apply a specific byte order to the incoming and outgoing values.

The following table describes the byte order code numbers:

For 4 byte values (single-precision floating point numbers and double words).

Code Number          Message Bytes          Assembled Order
1                               1 2 3 4                      1 2 3 4

2                               1 2 3 4                      2 1 4 3

3                               1 2 3 4                      3 4 1 2

4                               1 2 3 4                      4 3 2 1

For 8 byte values (double-precision floating point numbers).

Code Number         Message Bytes           Assembled Order
1                             1 2 3 4 5 6 7 8            1 2 3 4 5 6 7 8

2                             1 2 3 4 5 6 7 8            2 1 4 3 6 5 8 7

3                             1 2 3 4 5 6 7 8            3 4 1 2 7 8 5 6

4                             1 2 3 4 5 6 7 8            4 3 2 1 8 7 6 5

5                             1 2 3 4 5 6 7 8            5 6 7 8 1 2 3 4

6                             1 2 3 4 5 6 7 8            6 5 8 7 2 1 4 3

7                             1 2 3 4 5 6 7 8            7 8 5 6 3 4 1 2

8                             1 2 3 4 5 6 7 8           8 7 6 5 4 3 2 1

~

Append a '~' to the register to access the two's compliment of the data in the register.

!

Append a '!' to the register to perform a bit-wise NOT (all bits in the value are inverted) of the data in the register.

[n]

Append a '[n]' to the register to specify an array of registers of size n. This can be combined with all of the above conversion flags except '/', and is required for string conversions (flag 'M').

[nDS]

Append ‘[nDS]’ to a 16-bit register to specify an array of 16-bit registers of size n.  This will be a write only string of decimal values for each 16-bit register. The purpose of ‘[nDS]’ is to provide a Modbus write, where all the 16-bit registers are guaranteed to be in the same Modbus message. These decimal values are comma ‘,’ delimited. A minus sign ‘-’ is used to denote negative numbers, no sign should be used for positive numbers. ‘[nDS]’ may not be combined with any other conversions. OPC quality will be updated after the write succeeds or fails.

[nHS]

Append ‘[nHS]’ to a 16-bit register to specify an array of 16-bit registers of size n.  This will be a write only string of hexadecimal values for each 16-bit register. The purpose of ‘[nHS]’ is to provide a Modbus write, where all the 16-bit registers are guaranteed to be in the same Modbus message. These hexadecimal values are not delimited, so no commas or spaces are permitted between 16-bit register values.  There must be 4 hexadecimal characters for each 16-bit register, '0 to 9', 'A to F' or 'a to f'. ‘[nHS]’ may not be combined with any other conversions. OPC quality will be updated after the write succeeds or fails.

40001L

Access registers 40001 and 40002 as one 32-bit unsigned integer.

40001LS

Access registers 40001 and 40002 as one 32-bit signed integer.

40001[10]

Access registers 40001 through 40010 as an array of ten values.

40001L[10]

Access registers 40001 through 40020 as an array of ten 32-bit unsigned integers.

40001/0

Access bit 0 (the lowest bit) of register 40001.

40001/3.2

Access bits 3, 4 of register 40001.

40001F

Access registers 40001 and 40002 as one 32-bit single-precision floating point value.

40001F^2

Access registers 40001 and 40002 as one 32-bit single-precision floating point value and assemble the received data bytes in the following order: 2, 1, 4, 3.

40001M[6]

Access registers 40001 through 40003 as a string of 6 characters.

10001IS

Access 16 bits of memory as a two byte signed short integer starting at register 10001.

10001M[10]

Access registers 10001 through 10080 as a string of ten characters.

EXCSTATUS/1

Access bit 1 of the exception status byte.

EXCSTATUS/2.2

Access bits 2 and 3 of the exception status byte.

3001[10DS]

A write only decimal string for 10, 16-bit registers.  A valid value to write would be ‘1, 2, 3, 4,    5, -6, 7, 0, 122,14’.

3002[3HS]

A write only hexadecimal string for 3, 16-bit registers.  A valid value to write would be ‘1238BB0FCB41’.