Indigo202 supports the Modbus RTU serial communication protocol (2-wire RS-485 interface).
There are 2 groups of Modbus register addresses in use in Indigo202: probe registers and Indigo registers. The probe registers are received from the connected probe, and are organized according to the probe's register map. Indigo registers include transmitter-specific information.
| Address | Name | Data type |
|---|---|---|
| Probe registers (according to the connected probe's register map) 1 | ||
| 0x0000 | First measurement probe address | |
| 0xDFFF | Last measurement probe address | |
| Indigo registers | ||
| 0xE000 | Status | 16-bit |
| 0xE001 | Notification and error bits | 16-bit |
| 0xE002 | Connected probe | text [30] |
| 0xE011 | Relay A status | enum |
| 0xE012 | Relay B status | enum |
Received Modbus requests for register operations are handled in two different ways, depending on whether the register is a probe register or an Indigo transmitter register. Addresses above 0xDFFF (that is, Indigo registers) are handled as normal requests. Lower addresses (that is, probe registers 0x0000–0xDFFF) are passed to the measurement probe, and the response from the probe is again passed to the original Modbus client. Indigo can also have a cache for commonly requested registers (Measurement registers).
The maximum response delay is 2 seconds (when the data content needs to be fetched from the probe). The minimum delay between requests is 10 ms.