What is the formula for Modbus RTU Frame & CRC16?

Core formula: Frame = Slave + Function + Data + CRC16 (low byte first) | CRC-16/MODBUS init 0xFFFF. The tool returns results instantly using this formula and the selected parameters.

What engineering notes should I keep in mind when using Modbus RTU Frame & CRC16?

CRC-16/MODBUS covers everything except the CRC itself; the low byte is sent first. Standard RTU timing: inter-frame gap ≥ 3.5 char times (t3.5), intra-frame gap ≤ 1.5 char times (t1.5). Multi-byte fields (start address / quantity / register value) are always big-endian (high byte first). Coils/discretes are bit-packed: the LSB of the first byte is coil 0 (LSB first).

Modbus RTU Frame & CRC16

Favorite

Pack/unpack Modbus RTU frames (master request / slave response), compute the CRC-16/MODBUS checksum, and decode frames — matched against the standard frame format.

Key points

Modbus RTU Frame & CRC16: Pack/unpack Modbus RTU frames (master request / slave response), compute the CRC-16/MODBUS checksum, and decode frames — matched against the standard frame format. Formula: Frame = Slave + Function + Data + CRC16 (low byte first) | CRC-16/MODBUS init 0xFFFF. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. CRC-16/MODBUS covers everything except the CRC itself; the low byte is sent first. Standard RTU timing: inter-frame gap ≥ 3.5 char times (t3.5), intra-frame gap ≤ 1.5 char times (t1.5).

Inputs

Frame = Slave + Function + Data + CRC16 (low byte first) | CRC-16/MODBUS init 0xFFFF

ModeDirectionSlave addressSlave address: 1–247; 0 is broadcast (write only)Function codeStart addressRegister/coil start address (0-based; used for writes & echoed responses)QuantityFor read / write-multiple / response data: coils 1–2000, registers 1–125Coil / register valueWrite single (request & response): 05 = ON/OFF, 06 = 0–65535Data (bits / register values)Write-multiple or response: bit string (0F / read-coils response) or register list (10 / read-registers response), comma/space separated

Calculation model (updates with parameters)

Full frame (hex)	01 03 00 00 00 01 84 0A	Sent by master
CRC16	84 0A	0x0A84, low byte first
Data field	00 00 00 01	Start address 0, quantity 1
Frame length	8 字节	从站 1，Function code 03 (Read Holding Registers)，request

Engineering notes

CRC-16/MODBUS covers everything except the CRC itself; the low byte is sent first.
Standard RTU timing: inter-frame gap ≥ 3.5 char times (t3.5), intra-frame gap ≤ 1.5 char times (t1.5).
Multi-byte fields (start address / quantity / register value) are always big-endian (high byte first).
Coils/discretes are bit-packed: the LSB of the first byte is coil 0 (LSB first).

FAQ

What is Modbus RTU Frame & CRC16 for?: Pack/unpack Modbus RTU frames (master request / slave response), compute the CRC-16/MODBUS checksum, and decode frames — matched against the standard frame format.
What is the formula for Modbus RTU Frame & CRC16?: Core formula: Frame = Slave + Function + Data + CRC16 (low byte first) | CRC-16/MODBUS init 0xFFFF. The tool returns results instantly using this formula and the selected parameters.
What engineering notes should I keep in mind when using Modbus RTU Frame & CRC16?: CRC-16/MODBUS covers everything except the CRC itself; the low byte is sent first. Standard RTU timing: inter-frame gap ≥ 3.5 char times (t3.5), intra-frame gap ≤ 1.5 char times (t1.5). Multi-byte fields (start address / quantity / register value) are always big-endian (high byte first). Coils/discretes are bit-packed: the LSB of the first byte is coil 0 (LSB first).