Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
MODBUS_READ_REGISTER(3)	       libmodbus Manual	       MODBUS_READ_REGISTER(3)

NAME
       modbus_read_registers - read many registers

SYNOPSIS
       int modbus_read_registers(modbus_t *ctx,	int addr, int nb, uint16_t
       *dest);

DESCRIPTION
       The modbus_read_registers() function shall read the content of the nb
       holding registers to the	address	addr of	the remote device. The result
       of reading is stored in dest array as word values (16 bits).

       You must	take care to allocate enough memory to store the results in
       dest (at	least nb * sizeof(uint16_t)).

       The function uses the Modbus function code 0x03 (read holding
       registers).

RETURN VALUE
       The function shall return the number of read registers if successful.
       Otherwise it shall return -1 and	set errno.

ERRORS
       EMBMDATA
	   Too many registers requested

EXAMPLE
	   modbus_t *ctx;
	   uint16_t tab_reg[64];
	   int rc;
	   int i;

	   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;
	   }

	   rc =	modbus_read_registers(ctx, 0, 10, tab_reg);
	   if (rc == -1) {
	       fprintf(stderr, "%s\n", modbus_strerror(errno));
	       return -1;
	   }

	   for (i=0; i < rc; i++) {
	       printf("reg[%d]=%d (0x%X)\n", i,	tab_reg[i], tab_reg[i]);
	   }

	   modbus_close(ctx);
	   modbus_free(ctx);

SEE ALSO
       modbus_write_register(3)	modbus_write_registers(3)

AUTHORS
       The libmodbus documentation was written by StA(C)phane Raimbault
       <stephane.raimbault@gmail.com>

libmodbus v3.1.6		  08/10/2020	       MODBUS_READ_REGISTER(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLE | SEE ALSO | AUTHORS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=modbus_read_registers&sektion=3&manpath=FreeBSD+12.2-RELEASE+and+Ports>

home | help