FreeBSD Manual Pages
modbus_read_registers() modbus_read_registers() 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 hold- ing registers to the address addr of the remote device. The result of read- ing is stored in dest array as word values (16 bits). The dest array must be allocated with at least nb * sizeof(uint16_t) bytes. It is the caller's responsibility to ensure the buffer is large enough to hold all the registers to be read. The function uses the Modbus function code 0x03 (read holding registers). Return value The function shall return the number of read registers if successful. Oth- erwise it shall return -1 and set errno. Errors * EINVAL, the ctx or dest argument is NULL, or nb is less than 1. * EMBMDATA, too many registers requested (nb > MODBUS_MAX_READ_REGISTERS). Example modbus_t *ctx; uint16_t tab_reg[64]; int rc; int i; ctx = modbus_new_tcp("127.0.0.1", 502); 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 <modbus_write_register.md> * modbus_write_registers <modbus_write_registers.md> modbus_read_registers()
Name | Synopsis | Description | Return value | Errors | Example | See also
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=modbus_read_registers&sektion=3&manpath=FreeBSD+Ports+15.1.quarterly>