graham22
commented
6 years ago here is an update to that function, try replacing the attached ModbusLib.dll in C:\Program Files (x86)\SkyeTracker\ModbusSlave
/// <summary>
/// Append the typical header for a request command (master-side)
/// </summary>
/// <param name="command"></param>
/// <param name="body"></param>
internal static void PushRequestHeader(
ModbusCommand command,
ByteArrayWriter body)
{
body.WriteUInt16BE((ushort)command.Offset);
if (command.FunctionCode == 05 || command.FunctionCode == 06)
{
body.WriteInt16BE((short)command.Data[0]);
}
else
{
body.WriteInt16BE((short)command.Count);
}
}Graham.
On Tue, Dec 5, 2017 at 8:38 AM, Thomas van Lingen notifications@github.com wrote:
Hello once again, @graham22 https://github.com/graham22!
Similar to #4 https://github.com/graham22/ModbusTool/issues/4. A Non spec-compliant PDU is returned for the "Write Single Register" call when using the "Modbus Slave" tool.
Section 6.6 "06 (0x06) Write Single Register" of the Modbus Application Protocol document states the following:
The normal response is an echo of the request, returned after the register contents have been written.
Writing a value 0xAAAA to address 0x0000 using the "Write Single Register" Modbus function, the Modbus Slave tool sends me the following message (copied from the Communication log): TX: 00 01 00 00 00 06 01 06 00 00 00 01
Manually decoding it leads to the following:
Transaction ID: 0x0001 Protocol ID: 0x0000 Length: 0x0006 Unit ID: 0x01
Function Code: 0x06 Register Address: 0x0000 Register Value: 0x0001
The Register Value field is not equal to the written value (0xAAAA).
Going through the code, the bug seems to be in this https://github.com/graham22/ModbusTool/blob/master/ModbusLib/Protocols/Modbus/Codecs/ModbusCodecWriteSingleRegister.cs#L61 file in the ServerEncode method. Instead of the written register value being pushed into the message, the message header is (using the PushRequestHeader function). This deviates from the specification.
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-- Graham A. Ross (613) 769-1331
ThomasvLingen
Hello once again, @graham22!
Similar to #4. A Non spec-compliant PDU is returned for the "Write Single Register" call when using the "Modbus Slave" tool.
Section 6.6 "06 (0x06) Write Single Register" of the Modbus Application Protocol document states the following:
Writing a value
0xAAAAto address0x0000using the "Write Single Register" Modbus function, the Modbus Slave tool sends me the following response (copied from the Communication log):TX: 00 01 00 00 00 06 01 06 00 00 00 01Manually decoding it leads to the following:
The
Register Valuefield is not equal to the written value (0xAAAA).Going through the code, the bug seems to be in this file in the
ServerEncodemethod. Instead of the written register value being pushed into the message, the message header is (using thePushRequestHeaderfunction). This deviates from the specification.