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Fix modbus function 23 to conform with v1.1b3. #189

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Fix modbus function 23 to conform with v1.1b3. #189

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34 changes: 15 additions & 19 deletions modbus_tk/modbus.py
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Original file line number Diff line number Diff line change
Expand Up @@ -601,38 +601,34 @@ def _read_write_multiple_registers(self, request_pdu):
# get the starting address and the number of items from the request pdu
(starting_read_address, quantity_of_x_to_read, starting_write_address, quantity_of_x_to_write, byte_count_to_write) = struct.unpack(">HHHHB", request_pdu[1:10])

# read part
if (quantity_of_x_to_write <= 0) or (quantity_of_x_to_write > 121) or (byte_count_to_write != (quantity_of_x_to_write * 2)):
# maximum allowed size is 121 registers in one reading
raise ModbusError(defines.ILLEGAL_DATA_VALUE)

if (quantity_of_x_to_read <= 0) or (quantity_of_x_to_read > 125):
# maximum allowed size is 125 registers in one reading
LOGGER.debug("quantity_of_x_to_read is %d", quantity_of_x_to_read)
raise ModbusError(defines.ILLEGAL_DATA_VALUE)

# look for the block corresponding to the request
block, offset = self._get_block_and_offset(defines.HOLDING_REGISTERS, starting_read_address, quantity_of_x_to_read)
# look for the blocks corresponding to the request
write_block, write_offset = self._get_block_and_offset(defines.HOLDING_REGISTERS, starting_write_address, quantity_of_x_to_write)

# get the values
values = block[offset:offset+quantity_of_x_to_read]
read_block, read_offset = self._get_block_and_offset(defines.HOLDING_REGISTERS, starting_read_address, quantity_of_x_to_read)

# write data to the write block
for i in range(quantity_of_x_to_write):
fmt = "H" if self.unsigned else "h"
write_block[write_offset+i] = struct.unpack(">"+fmt, request_pdu[10+2*i:12+2*i])[0]

# get the values from the read block
values = read_block[read_offset:read_offset+quantity_of_x_to_read]
# write the response header
response = struct.pack(">B", 2 * quantity_of_x_to_read)
# add the values of every register on 2 bytes
for reg in values:
fmt = "H" if self.unsigned else "h"
response += struct.pack(">"+fmt, reg)

# write part
if (quantity_of_x_to_write <= 0) or (quantity_of_x_to_write > 123) or (byte_count_to_write != (quantity_of_x_to_write * 2)):
# maximum allowed size is 123 registers in one reading
raise ModbusError(defines.ILLEGAL_DATA_VALUE)

# look for the block corresponding to the request
block, offset = self._get_block_and_offset(defines.HOLDING_REGISTERS, starting_write_address, quantity_of_x_to_write)

count = 0
for i in range(quantity_of_x_to_write):
count += 1
fmt = "H" if self.unsigned else "h"
block[offset+i] = struct.unpack(">"+fmt, request_pdu[10+2*i:12+2*i])[0]

return response

def _mask_write_register(self, request_pdu):
Expand Down