In-Situ Aqua TROLL 400 Modbus and SDI-12 Reference Guide - Manual (Page 76)

8.31 Baud Rates
The instrument supports 9600 through 57600 baud rates. A device will support all baud rates
from 9600 up to and including the maximum baud rate as specified by the Max Baud Rate ID
register.
•
If the Master attempts to set the baud rate of a device to a non-supported value, the
device will respond with a Modbus exception error code 3 (Illegal Data Value).
•
Baud rates will be referenced in this document by the ID 0-7.
8.32 RTU Settings
Every device supporting serial communications will implement Modbus RTU. The device will at
a minimum support the standard settings defined below.
• 1 Start Bit
• 8 Data Bits
• 1 Parity Bit
• 1 Stop Bit
• Even Parity
Note: If an attempt is made to write RTU mode with 7 data bits, the device will return an
exception with error code 0x84 (Write Illegal Value). RTU communication does not
support 7-data-bit settings.
8.33 ASCII Settings
When implementing Modbus ASCII, the device will at a minimum support the standard settings
defined below.
• 1 Start Bit
• 7 Data Bits
• 1 Parity Bit
• 1 Stop Bit
• Even Parity
8.34 Max Message/Response Size
This register indicates to the Master the largest message or response the device can accept.
This may vary based on the hardware configuration of the device.
8.35 Message Counters
The message counter registers are to provide diagnostic information for troubleshooting
communication problems. The counters will not roll over and can only be cleared using the
configuration software.
There are 3 message counter registers allocated as follows:
• Good Message Counter – count of number of properly formatted messages received
that are addressed to this device.
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