AT Command to change frame size gives ERROR

Question

I'm using a SIM900A GSM Shield to communicate between an arduino due and an API. I currently using it's default values in the multiplexer of GSM Shield. But now I'm in need of changing it's frame size to 255. When I check the current frame size, it gives following response which indicates the frame size as 127.

CMUX Read:AT+CMUX?

+CMUX: 0,0,5,127,10,3,30,10,2
OK

Then I used following AT command to change it to 255. But it gives an ERROR.

sim900_send_cmd("AT+CMUX=0[,0[,1[,255[,10[,3[,30[,10[,2]]]]]]]]\r\n");

CMUX Read:AT+CMUX=0[,0[,5[,255[,10[,3[,30[,10[,2]]]]]]]] 
ERROR 

What am I doing wrong here ? am I missing a step ? Any insight will be much appreciated. Thank you

Answer 1

I'm not an expert in AT commands, but I bet you don't need all the brackets in yours. Brackets are used to indicate parameters which could be omitted. So your command should look like this:

CMUX Read:AT+CMUX=0,0,5,255,10,3,30,10,2

Maybe even a shoter version will work:

CMUX Read:AT+CMUX=0,0,5,255