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Manual Reference Pages  -  MODBUS_SEND_RAW_REQUEST (3)

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NAME

modbus_send_raw_request - send a raw request

CONTENTS

SYNOPSIS

int modbus_send_raw_request(modbus_t *ctx, uint8_t *raw_req, int raw_req_length);

DESCRIPTION

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.

RETURN VALUE

The modbus_send_raw_request() function shall return the full message length, counting the extra data relating to the backend, if successful. Otherwise it shall return -1 and set errno.

EXAMPLE

modbus_t *ctx;
/* Read 5 holding registers from address 1 */
uint8_t raw_req[] = { 0xFF, 0x03, 0x00, 0x01, 0x0, 0x05 };
int req_length;
uint8_t rsp[MODBUS_TCP_MAX_ADU_LENGTH];

ctx = modbus_new_tcp("127.0.0.1", 1502); if (modbus_connect(ctx) == -1) { fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno)); modbus_free(ctx); return -1; }

req_length = modbus_send_raw_request(ctx, raw_req, 6 * sizeof(uint8_t)); modbus_receive_confirmation(ctx, rsp);

modbus_close(ctx); modbus_free(ctx);

SEE ALSO

modbus_receive_confirmation(3)

AUTHORS

The libmodbus documentation was written by St\(&#146;ephane Raimbault <\m[blue]stephane.raimbault@gmail.com\m[][1]>

NOTES

1. stephane.raimbault@gmail.com  mailto:stephane.raimbault@gmail.com
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libmodbus 3&.1&.0 MODBUS_SEND_RAW_REQU (3) 10/06/2013

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