5. Modbus
5.1 Modbus Overview
Indigo 202 supports the Modbus RTU serial communication protocol (2-wire RS-485
interface).
There are 2 groups of Modbus register addresses in use in Indigo 202: 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.
Table 3 Indigo 202 Modbus Registers
Address
Name
Data Type
Probe registers (according to the connected probe's register map)
0000
hex
First measurement probe address
DFFF
hex
Last measurement probe address
Indigo registers
E000
hex
Status
16-bit
E001
hex
Notification and error bits
16-bit
E002
hex
Connected probe
text [30]
E011
hex
Relay A status
enum
E012
hex
Relay B status
enum
1)
See the connected probe's Modbus documentation for probe-specific register information
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 DFFF
hex
(that is, Indigo registers) are handled as normal requests. Lower
addresses (that is, probe registers 0000
hex
... DFFF
hex
) 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.
More Information
‣
Modbus Serial Communication Settings (page 34)
‣
‣
Indigo Status Registers (page 65)
Chapter 5 – Modbus
39
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