Woodward 505XT, Инструкция по установке и эксплуатации

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Manual 35018V1 505XT Digital Control System for Steam Turbines
Woodward 198
Table 6-2. Modbus Frame Definition
Beginning
of Frame
Slave
Address
Function
Code
Data Error
Check
Code
End of
Frame
ASCII
: 2 CHARS
8 BITS
2 CHARS
8 BITS
4 BITS
DATA PER
CHAR
2 CHARS
8 BITS
CR LF
RTU
3-CHAR
DEAD TIME
1 CHAR
8 BITS
1 CHAR
8 BITS
8 BITS
DATA PER
CHAR
2 CHAR
16 BITS 3 CHAR
DEAD TIME
The Modbus function code tells the addressed slaves what function to perform. The following table lists
the function codes supported by this control.
Table 6-3. Modbus Function Codes
Code Definition Reference Address
01 Read Digital Outputs (Raise/Lower and Enable/Disable
Commands)
0XXXX
02 Read Digital Inputs (Status Indications/Alarms and Trips) 1XXXX
03 Read Analog Outputs 4XXXX
04 Read Analog Inputs (Speed, Setpoint, etc.) 3XXXX
05 Write Single Discrete Output (Raise/Lower and Enable/Disable
Commands)
0XXXX
06 Write Single Register (Enter Setpoint Directly) 4XXXX
08 Loopback Diagnostic Test (Subfunction 0 only) N/A
15 Write Digital Outputs 0XXXX
16 Write Analog Outputs 4XXXX
When a Modbus message is received, it is checked for any errors or invalid data. If there is invalid data in
the message, an error code is sent back to the master and the control issues an alarm message. The
error codes are defined in the following table. The exception error status and respective error codes can
be viewed on the Communication pages under the Service Menu.
If the control has not received a message for the configured time-out period, the control will alarm with an
error message, but no message is sent to the master. This time-out is defaulted to 2 seconds and only
applies to units using both monitor and control (adjustable through the Service Menu).
Table 6-4. Modbus Error Codes
Error
Code Error
Message Code Sent
To Master
Description
0 No Error 0 No Error
1 Bad Modbus function 1 The specified function is not supported for this control.
2 Bad Modbus data address 2 The Modbus value addressed is not valid for this control.
3 Bad Modbus data value 3 Too many values requested or the on/off indicator in
function code 5 is invalid.
9 Bad Modbus checksum None Message checksum did not match.
10 Bad Modbus message None Message could not be decoded.
N/A Lost Modbus link None No messages received for the configured time-out period