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Error Messages
The Modbus protocol provides for the return of error codes in the event of a data error within a correctly
formatted message block. When the Viltech controller detects an error within a read or write message, the message
response will contain an error code instead of the expected data response.
The following example shows an error response to an illegal data value in a Preset Multiple Registers command.
NOTE: 0x80 has been added to the function code.
The following error codes are supported:
Data Formats
For Modbus communications, 16-bit messages are transmitted with the lower 8-bits first followed by
the upper 8-bits.
Real number data is represented in 16-bit signed integer format with one or less implied decimal points.
For example, the number 127.3 would be stored as 1273 decimal or 04F9 hex. Negative numbers are stored
in two’s complement form. For example, -237.4 would be stored as -2374 decimal or F6BA hex.
The Discrete I/O parameters are transmitted in a packed binary format where each bit represents an
individual input or output. Data marked as optional only applies to RECIP compressors with optional
equipment installed.
The Alarm data includes all alarm, failure, and OEM failure conditions currently active on the compressor. The
data is transmitted in a packed binary format where each bit represents an individual alarm. Each alarm is assigned
one of the following three levels:
• Alarm -The parameter is outside of the normal operating range.
• Fail - Similar to alarm but may cause RECIP to shutdown.
• OEM - A failure caused by parameters exceeding the manufacturer’s safety limits.
The Equipment data contains important information about the equipment on the microcontroller. This information
is packed into a data block which mixes several types and formats of data.
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