modbus Hex address Conversion

Question

I am trying to read data from GE-PQM II energy meter. Energy meter supports real time monitoring via 2 wire RS-485 MODBUS connection. I use libmodbus library in c to read modbus registers.

In GE communication guide (https://www.ccontrols.com/support/dp/GEK-113532.pdf) the address of the register are given in hexadecimal. I converted hex to decimal.

I am trying to read values from modbus register (02F0,02F1) - corresponding decimal values are 752,753

GE-PQM sample

My code:

rc = modbus_read_registers(ctx, 752, 753, clock);

output :

ERROR Too many registers requested (753 > 125)
Too many data

Anything wrong in hex conversion ? or some where else?

Did you actually read the documentation for modbus_read_registers? When there is an error, the first thing to do should be to consult the documentation. Check what the third parameter is supposed to be. — kaylum
If you use this libmodbus, so in function call int modbus_read_registers(modbus_t *ctx, int addr, **int nb**, uint16_t *dest); parameter nb is number of register for read and it must be equal 2 and not 753. — imbearr
No need to convert to decimal either, just use 0x2F0 for address. — Mark Tolonen

Unknown Unknown · Accepted Answer · 2016-07-21T09:42:22

If you use this libmodbus, so in function call

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

nb

modbus Hex address Conversion

1 Answers