Sigma Programmable Object Bit Mask to Decode Modbus Register

[Product_Support]

Issue

How to decode individual on/off states from a Modbus analogue register (e.g., Holding or Input registers) using bit masking. Each bit represents the status of a coil and needs to be read separately.

Product Line

Satchwell Sigma Software

Environment

Sigma IC Modbus and IC3 Modbus controllers

Cause

Modbus registers are 16-bit values. Each bit (0 or 1) represents the on/off state of a coil. To interpret these states, bit masking is used to isolate and evaluate each bit.

Resolution

Each Modbus register contains 16 bits. For example, a value of 901 in Sigma translates to the binary 0000001110000101, where:

• 1 = ON
• 0 = OFF

To decode each bit:

1. Create a Sigma analogue input object to read the Modbus value.
2. Create a programmable object for each bit (up to 16 per register).

---

Example Code Snippets

Assuming POINT 0|222 is the Modbus value object, here’s how to decode each bit:

Bit 1 (LSB)

10 XINT = INT POINT 0|222
20 YINT = XINT MASK ( 1 )
30 IF YINT = 1 THEN RETURN TRUE "Bit 1 = on"
40 RETURN FALSE "Bit 1 = off"

Bit 2

10 XINT = INT POINT 0|222
20 YINT = XINT MASK ( 2 )
30 IF YINT = 2 THEN RETURN TRUE "Bit 2 = on"
40 RETURN FALSE "Bit 2 = off"
``

Bit 3 to Bit 16

Repeat the pattern above, updating the mask value as follows:

Bit	Mask Value
3	4
4	8
5	16
6	32
7	64
8	128
9	256
10	512
11	1024
12	2048
13	4096
14	8192
15	16384
16 (MSB)	32768