Super Systems AC20 RS485 Modbus - Manual (Page 10)

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TITLE: MODBUS/J-BUS Protocol for SSi’s- AC20 ENG. 824E REV. 1
Function code 15: Multiple bits writing
This function code is used by master unit to set/reset a consecutive group of bits (max 24).
Command from master to slave Reply from slave to master
Range Byte Range Byte
Slave address (0*-255) 1 Slave address (1-255) 1
Function code (15) 1 Function code (15) 1
Bit starting address (high byte) 1 Bit starting address (high byte) 1
Bit starting address (low byte) 1 Bit starting address (low byte) 1
Number of bits (high byte) 1 Number of bits (high byte) 1
Number of bits (low byte) 1 Number of bits (low byte) 1
Byte counter (n) 1 Error check (CRC-16) (low byte) 1
Data n Error check (CRC-16) (high byte) 1
Error check (CRC-16) (low byte) 1
Error check (CRC-16) (high byte) 1
* To use the address 0, see note 1 at page 12: “Broadcast address”.
The desired status of each bit is packed in the DATA field (1 = ON, 0 = OFF).
The status imposed for read only bits will be ignored.
The command will be processed starting from the first bit and it will be executed or not
executed depending on the actual device status.
At the first error found, the command will be aborted and the slave will answer with an
error.
Example:
Send to slave, at address 2 (2h), the following set of 9 bits:
bit 224 status = 0
(bit 0) bit 232 status = 1 (bit 0)
bit 225 status = 1 (bit 1) Don’t care = 0 (bit 1)
bit 226 status = 1 (bit 2) Don’t care = 0 (bit 2)
bit 227 status = 0 (bit 3) Don’t care = 0 (bit 3)
bit 228 status = 1 (bit 4) Don’t care = 0 (bit 4)
bit 229 status = 0 (bit 5) Don’t care = 0 (bit 5)
bit 230 status = 1 (bit 6) Don’t care = 0 (bit 6)
bit 231 status = 1 (bit 7) Don’t care = 0 (bit 7)
NOTE: 2 bytes with 9 bits and 7 don’t care bits must be sent
Command from master to slave Reply from slave to master
Range Byte Range Byte
Slave address 02h Slave address 02h
Function code 0Fh Function code 0Fh
Bit starting address (high byte) 00h Bit starting address (high byte) 00h
Bit starting address (low byte) E0h Bit starting address (low byte) E0h
Number of bits (high byte) 00h Number of bits (high byte) 00h
Number of bits (low byte) 09h Number of bits (low byte) 09h
Byte counter 02h Error check (CRC-16) (low byte) 94h
Data D6h Error check (CRC-16) (high byte) 08h
Data 01h
Error check (CRC-16) (low byte) 78h
Error check (CRC-16) (high byte) 4Ch