B-18 F650 DIGITAL BAY CONTROLLER GEK-106310-AF
B.4 MODBUS DATA APPENDIX B: MODBUS PROTOCOL
with its request, and special attention must be paid to setting confirmation writings, especially with reference to time-out.
EnerVista 650 Setup software is recommended to do the configuration modifications, as this software takes into account
all these details.
B.4.12 Traces and troubleshooting
The tracer is a debugging tool to view the strings in any writing or reading process in ModBus. This tracer is activated in the
menu from EnerVista 650 Setup: View, Traces.
With this option enabled, request and response strings are shown. If, for instance, the request and response strings view is
desired, between F650 and the relay, do the following:
1 - Activate traces, from View > Traces, and a new window opens at the bottom of the main window.
2 - Open the general settings menu: Setpoint > System Setup > General Settings
The screen displays the group settings, and on the left side bottom the relay read request is shown:
<0001><06/18/03 12:14:15>[0xFE 0x03 0x21 0x8A 0x00 0x16 0xFB 0xDD]
On the right the settings response is shown:
0001><06/18/03 12:14:15>[0xFE 0x03 0x2C 0x3F 0x80 0x00 0x00 0x3F 0x80 0x00 0x00 0x3F 0x80 0x00 0x00 0x3F
0x80 0x00 0x00 0x00 0x00 0x42 0xC8 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x00 0xFE
0x00 0xFE 0x00 0x06 0x00 0x06 0x00 0x00 0x01 0xF6 0xAC 0xB5]
This way, any request or mechanism to obtain information from the relay can be viewed string by string.
There is another tool for tracing the relay memory: in the EnerVista 650 Setup menu: Communication > Troubleshooting,
any read of any address can be requested, and the PC forms the request string together with the check-sum register.
B.4.13 MODBUS CRC generation function
This section describes the C programming language implementation to calculate the CRC of the message string check in
ModBus, in a Big-Endian format.
The implemented function in the F650 called here fn_035c_cr16 returns an unsigned 16 bit type (2 bytes) with the CRC of
the message defined in the function parameters as:
p = pointer to the MODBUS message string to calculate the CRC
us = length in bytes of the MODBUS message (header + data) minus 2 bytes (the CRC of the message itself)
USHORT fn_035c_cr16(UCHAR *p, UNSIGNED us)
{
const UCHAR hi[] = {
0X0,0Xc1,0X81,0X40,0X1,0Xc0,0X80,0X41,0X1,0Xc0,
0X80,0X41,0X0,0Xc1,0X81,0X40,0X1,0Xc0,0X80,0X41,
0X0,0Xc1,0X81,0X40,0X0,0Xc1,0X81,0X40,0X1,0Xc0,
0X80,0X41,0X1,0Xc0,0X80,0X41,0X0,0Xc1,0X81,0X40,
0X0,0Xc1,0X81,0X40,0X1,0Xc0,0X80,0X41,0X0,0Xc1,
0X81,0X40,0X1,0Xc0,0X80,0X41,0X1,0Xc0,0X80,0X41,
0X0,0Xc1,0X81,0X40,0X1,0Xc0,0X80,0X41,0X0,0Xc1,
0X81,0X40,0X0,0Xc1,0X81,0X40,0X1,0Xc0,0X80,0X41,
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