B&B Electronics Vlinx MESR9xx - Manual (Page 29)

4. Properties Vlinx MESR9xx Modbus Gateway
Page 25 Manual Documentation Number MESR9xx-4508m
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Modbus ASCII
The Modbus ASCII message protocol is a human readable version of the Modbus
message, and is one of the three Modbus formats supported by the MESR9xx Modbus
Gateway.
A major advantage of Modbus ASCII is it allows up to a 1 second gap between bytes. It
uses a Longitudinal Redundancy Check (LRC) checksum to verify message accuracy.
Modbus Message Buffering
The MESR9xx has two Modbus serial buffers, one for each serial port. Each will buffer
up to 32 Modbus messages. These buffers help ensure messages don’t get lost in a data
traffic jam, and are part of what makes Modbus such an outstandingly reliable serial
protocol.
Modbus Message Timeout
Message timeout is supported by the MESR9xx. This is the maximum amount of time
before a response to a message is expected.
Modbus RTU Message
The Modbus RTU message is broken into 4 different parts. The address field, the
function code, this is copied directly over from the Modbus TCP message, the data and
the error check, a 16 bit cyclic redundancy check or CRC.
Modbus Serial Control
Message Timeout
The message timeout is the maximum time the gateway allows for a response from the
slave device. The default is 1000ms.