APS 6RL Series, Руководство по эксплуатации

Страница: 126 / 204

6RL SERIES OPERATION MANUAL
SECTION 7: REMOTE PROGRAMMING
Entire Contents Copyright

2018 by Adaptive Power Systems, Inc. (APS) • All Rights Reserved • No reproduction without written authorization from APS.
6RL Series Regenerative DC Load Operation Manual Page 126 of 204
Byte 0 Byte 1 Bytes 2+3 Bytes 4+5 Bytes 6+7
Addr FC Start reg. Data CRC
0x00 0x05 0...65535 Written value echoed Checksum ModBus-CRC16
(1
Expected response for WRITE Multiple Registers:
Byte 0 Byte 1 Bytes 2+3 Bytes 4+5 Bytes 6+7
Addr FC Start reg. Data CRC
0x00 0x10 0...65535 Number of written registers Checksum ModBus-CRC16
(1
Expected response for READ Holding Registers:
Byte 0 Byte 1 Byte 2 Bytes 3-253 Letzte 2 Bytes
Addr FC Data length in bytes Data CRC
0x00 0x03 2...250 Queried registers content Checksum ModBus-CRC16
(1
Expected response for READ Coils:
Byte 0 Byte 1 Byte 2 Bytes 3+4 Bytes 5+6
Addr FC Data length in bytes Data CRC
0x00 0x01 2
Queried bit as 1 register
(always 16 coils)
Checksum ModBus-CRC16
(1
Unexpected response (communication error):
Byte 0 Byte 1 Byte 2 Letzte 2 Bytes
Addr FC CRC
0x00 Function code + 0x80 Error code Checksum ModBus-CRC16
(1
Note: A communication error can have several reasons, like a wrong checksum or when
attempting to switch a unit to remote control that has been set to “Local” or if it is
already remotely controlled by another interface. See the communication error
code list in section 7.9.4, “Communication Errors” on page 127.
7.9.3 The ModBus Checksum
The checksum at the end of ModBus RTU messages is a 16 bit checksum, but is not
calculated as the usual CRC16 checksum. Furthermore, the byte order of the checksum in
the message is reversed. Information about ModBus CRC16 and source code for
implementation and calculation are available on the Internet, for example here:
http://www.modbus.org/
Sample C Code:
// Compute the MODBUS RTU CRC
UInt16 ModRTU_CRC(byte[] buf, int len)
{
UInt16 crc = 0xFFFF;
for (int pos = 0; pos < len; pos++) {
crc ^= (UInt16)buf[pos]; // XOR byte into least sig. byte of crc
for (int i = 8; i != 0; i--) { // Loop over each bit
if ((crc & 0x0001) != 0) { // If the LSB is set
crc >>= 1; // Shift right and XOR 0xA001
crc ^= 0xA001;