ModBus: Supported functions
The following table lists the ModBus functions supported in SPLat, with a brief description of the function. This is not meant as a detailed treatment of ModBus; you should refer to the published specifications online at places like modbus.org. The hotlinks in the M/S column take you to the corresponding ModBus master script command (described later).
| Function | Name | M/S | Modicon ref | Description |
|---|---|---|---|---|
| 1 | Read Coil(s) | M S | 0xxxx | Reads out one or more contiguous coils (external outputs or internal 1-bit variables, i.e. semaphores) |
| 2 | Read inputs | M S | 1xxxx | Reads one or more contiguous inputs. In a slave SPLat accesses the debounced inputs. |
| 3 | Read holding registers | M S | 4xxxx | Reads one or more contiguous Modicon type 16-bit holding registers. In a SPLat slave the addresses are mapped to RAM (data memory). |
| 4 | Read input registers | M | 3xxxx | Reads one or more contiguous Modicon type 16-bit input registers. Some 3rd party products map internal values to these registers. Not supported in SPLat slave. |
| 5 | Force single coil | M S | 0xxxx | Forces a single coil (Modicon: external output or internal 1-bit variable, i.e. semaphore). Force external outputs with caution! SPLat slave allows selective write protection. |
| 6 | Preset single holding register. | M S | 4xxxx | Forces a value into a single Modicon type 16-bit holding register. In a SPLat slave the addresses are mapped to RAM (data memory). |
| 15 | Force multiple coils | M S | 0xxxx | Forces one or more contiguous coils (external outputs or internal 1-bit variables, i.e. semaphores). Force external outputs with caution! |
| 16 | Preset multiple holding registers. | M S | 4xxxx | Forces data values into one or more Modicon type 16-bit contiguous holding registers. In a SPLat slave the addresses are mapped to RAM (data memory). |