RTU Communication Time Estimator

Estimate FC03/04 read time and the continuous polling period for multiple devices.

Total wait from the end of a request to the start of its response; at least t3.5.

Wait from the end of a response to the next request. Enter 0 for only the minimum t3.5 gap.

Communication timeline45.833333 ms
1. Request transmission
9.166667 ms
2. Effective device wait
4.010417 ms
3. Response transmission
28.645833 ms
4. Effective request interval
4.010417 ms

Request: 8 bytes; response: 25 bytes; 11 bits per character.

t3.5 is 3.5 characters up to 19200 baud, then 1.75 ms. A cycle includes transmission and both waits. Polling includes the gap from the last device to the next round.

How to use

Each device receives the same normal read request. This theoretical estimate excludes retries, timeouts and computer or USB delays.

1–125 registers, 1–247 devices. Each wait: 0–3,600,000 ms. Maximum 64 characters per input.

Request: 8 bytes; response: 25 bytes; 11 bits per character.

9600 · 8E1: (8 + 25) × 11 ÷ 9600 × 1000 = 37.8125 ms
37.8125 + 4.010417 + 4.010417 ≈ 45.833333 ms

Modbus Serial Line V1.02