GPIB communication with instrument

Hi All,

I have been able to connect to an instrument (pressure volume controller), and read using GPIB (IEEE, NI GPIB-USB-HS) with:

obj1 = gpib('ni',0,3);

fopen(obj1)

data=fscanf(obj1);

p =data(1:5)
v =data(6:10)

fclose(obj1)
delete(obj1)
clear obj1

In the manufacturers documentation, to decrease the volume of the instrument by one step the following output (hexadecimal) is required to be written to the instrement:

40 0D 0A

Any advice on how best to achieve this?

Thanks in advance.