Register syntax reference

Expression form

${REG[@DEVICE][:TYPE]}

Part	Required	Description
REG	Yes	Register address in Modicon or prefix notation (see below)
@DEVICE	No	Device ID to read from. Defaults to device 1 if omitted
:TYPE	No	Data type. Defaults to 16b if omitted. Ignored for coils and discrete inputs

Examples

Expression	Meaning
${40001}	Holding register 40001, unsigned 16-bit, device 1
${40001: s16b}	Holding register 40001, signed 16-bit, device 1
${40001@2: 32b}	Holding register 40001, unsigned 32-bit, device 2
${i0}	Input register at address 0, unsigned 16-bit, device 1
${c5@3}	Coil 5, device 3

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Address notation

Two notations are supported and can be mixed in the same session.

Modicon 5-digit notation

Encodes the object type and address in one number. Limited to addresses 1–9999 within each type.

Range	Object type	Modbus function code
1 – 9999	Coil	1
10001 – 19999	Discrete input	2
30001 – 39999	Input register	4
40001 and above	Holding register	3

Address 40001 in Modicon notation maps to Modbus address 0 on the wire.

Prefix notation

Use a letter prefix followed by the full 0–65535 address. Required when the address exceeds 9999 within its type.

Prefix	Object type	Modbus function code
c0 – c65535	Coil	1
d0 – d65535	Discrete input	2
i0 – i65535	Input register	4
h0 – h65535	Holding register	3

ModbusScope stores addresses in Modicon notation when they fit; otherwise it uses prefix notation.

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Data types

Applies to holding registers and input registers only.

Type	Size	Signed	Notes
16b	16-bit	No	Default
s16b	16-bit	Yes
32b	32-bit	No	Two consecutive registers
s32b	32-bit	Yes	Two consecutive registers
f32b	32-bit	IEEE 754 float	Two consecutive registers

The byte order of 32-bit types is controlled by the 32-bit little-endian setting on the device. See Device settings.

For coils and discrete inputs, :TYPE is accepted but ignored. The result is always 0 or 1.