A Modbus TCP server and simulator on your iPhone
Start a server with an editable register map and test your SCADA, HMI or client code against it over Wi-Fi, with no PLC on the bench.
How it works
- Open Server, keep port
1502and tap Start. - Point an external Modbus TCP client at the iPhone's address on the same Wi-Fi network.
- Watch Active clients, the counters and the request log.
- Tap Stop when you finish. Open sessions close.
An editable register map
Coils and holding registers are writable, by you on screen and by clients through 05, 06, 15 and 16. Discrete inputs and input registers are read-only for clients.
A value written by a client appears in the map about twice a second while the screen is open and survives Stop and Start. A saved profile can seed the map when you ask it to.
Real exception answers
The server answers 01 for an unsupported function, 02 for an address outside the map, 03 for a bad quantity or byte count, and 04 for an internal failure. You can test how your client handles each error without breaking a PLC.
Limits you should plan for
- It runs in the foreground. Keep the app open on screen during a test.
- Port
1502is the default. iOS doesn't guarantee port502. - It speaks Modbus TCP only, without RTU over TCP.
- It is a test tool. Keep production traffic on a real gateway.
Before you buy
Can a PC connect to the iPhone?
Yes, if both are on the same network and iOS allows Local Network access for the app. Use the address the Server screen shows and port 1502.
Why not port 502?
Port 502 is the well-known Modbus port, and iOS doesn't guarantee an app can listen on it. If your client insists on 502, run a simulator on a laptop instead.
Can the same app be a client and a server?
It has both modes. For a test between two devices, run the server on one and the client on the other.
Test against a device you control
$5.99 once. Client and server are both included.