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The _modbus_receive_confirmation()_ function shall receive a request via the socket of the context 'ctx'. This function must be used for debugging purposes because the received response isn't checked against the initial request. This function can be convenient to receive request not handled by the library.
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The _modbus_send_raw_request()_ function shall send a request via the socket of the context 'ctx'. This function must be used for debugging purposes because you have to take care to make a valid request by hand. The function only adds to the message, the header or CRC of the selected backend, so 'raw_req' must start and contain at least a slave/unit identifier and a function code. This function can be used to send request not handled by the library.
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Inspired by the branch ff/ipv6 of Florian Forster but this version uses a specific PI backend to isolate the IPv4 and IPv6 implementations. The existing TCP/IPv4 implementation has been kept intact (not rebased on the PI one) because its data backend requires fewer bytes than the PI. New functions modbus_new_tcp_pi, modbus_tcp_pi_listen and modbus_tcp_pi_accept and new backend called modbus_tcp_pi_t.
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Page 38 in the document Modbus_Application_Protocol_V1_1b.pdf: 6.17 23 (0x17) Read/Write Multiple registers This function code performs a combination of one read operation and one write operation in a single MODBUS transaction. The write operation is performed before the read. The unit test has been updated.
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Contributed by Dominic Storey. - new function modbus_reply_exception - unit test
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The goal of this rewriting is to avoid the timeouts on the receiving of exceptions and to be more robust on bad requests. Some devices use the exception MODBUS_EXCEPTION_ACKNOWLEDGE to response to some valid requests, so in this case, you'll really appreciate this change! - Slower! More system calls are used. - The code is cleaner and easier to understand. - Really faster when an exception occurs. - Fix unit test of bad request in RTU
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These functions have no meaning in RTU so it's better to specialize the names and remove them from the backend. - remove the functions from the backend - update tests to handle RTU mode (master and slave) - add command line options to tests (rtu or tcp)
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- check strlcpy in configure.ac - test for empty device string - test truncated device string
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modbus_set_slave must be used to set the slave ID of the remote device to talk in master mode and to set the internal slave ID in slave mode. If you talk to several devices, you need to call modbus_set_slave each time the following requests must be sent to another device.
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- return only useful data client side - available in TCP when a gateway to RTU is used - need to add isolated handling of indication/confirmation messages