7 ED 15121
Valid Error Codes
The MicroTech III Chiller Unit Controller supports all exception codes. See Table 2 below for a description of valid
error codes.
Table 2. Valid Error Codes
Error Codes Description Definition
01 Illegal Function The function code received in the query is not an allowable action for the server (or slave).
02 Illegal Data Address The data address received in the query is not an allowable address for the server (or slave).
03 Illegal Data Value A value contained in the query data field is not an allowable value for server (or slave).
04 Slave Device Failure
An unrecoverable error occurred while the server (or slave) was attempting to perform the
requested action.
05 Acknowledged The server (or slave) is has accepted, and is processing, the request.
06 Slave Device Busy
The server (or slave) is busy processing a command. The client (or master) should retransmit
when the server (or slave) is free.
08 Memory Parity Error
The server (or slave) attempted to read record file, but detected a parity error in the memory.
The client (or master) can retry the request, but service may be required on the server (or
slave) device.
0A
Gateway Path
Unavailable
The gateway may be configured incorrectly or overloaded.
0B
Gateway Target Device
Failed to Respond
No response from the target device.
Modbus Addressing
Each function code implies access to a specific Modbus reference set. Therefore, the leading digit is not included in the
address field of a Modbus message. The Modbus Communication Module supports zero-based addressing. For
example, holding register 40003 is addressed as 0002 in a Modbus message.
Modbus Data Point
Each data point accessible from a Modbus network is described with a table that gives the data type and holding register.
If the data point represents an enumerated variable, the enumerations are also listed.
When a variable is spans multiple Holding Registers, it is important to know how the data is represented in those
Holding Registers. This is best shown with an example. Let’s use Compressor Run Hours. Circuit 1, compressor 1 run
hours is located at holding registers 74-75 (40074-40075). If the operating hours is 99900 (0x0001 0x863C), the
registers will be as follows:
• 74= 0x863C
• 75 = 0x0001
For strings, the interpretation differs. In this case, each holding register can contain two characters. If a string spans
multiple registers, the first register (lowest register number) contains the 2 left-most characters of the string. Since the
MicroTech III Chiller Unit Controller only supports Modbus RTU, use Appendix A: ASCII Character to translate the
numerical data to their corresponding ASCII characters. An example of registers that contain string data is Application
Version which is located at holding registers 334-338 (40334-40338). The following example shows the holding register
and its value (in hexadecimal), followed by the ASCII character translation.
• 334= 0x3235
• 0x32 = “2”
• 0x35 = “5”
• 335= 0x3035
• 0x30 = “0”
• 0x35 = “5”
• 335= 0x3036
• 0x30 = “0” Application Version = 2505067100
• 0x35 = “6”
• 337= 0x3731
• 0x37 = “7”
• 0x31 = “1”
• 338= 0x3030
• 0x30 = “0”
• 0x30 = “0”
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