21
Command Mode continued:
<CHK> stands for CHECKSUM: the <CHK> value is
calculated by performing an XOR of the full com-
mand string. For example: //F00M12I03 will XOR
to the hexadecimal value 0x42, therefore the value
of <CHK> is 0x42.
CALCULATING THE <CHK>
IMPORTANT
5) To query crosspoints from PC:
//FxxU<CHK><CR>
• If all outputs are connected to input 1 then a 4x4 Matrix will respond
with
<0x80><0x80><0x80><0x80><CR>
• The router will send back one byte for each output and the string
ends with a <CR>. The first byte sent is Output #1. In the example
above, since there are 5 bytes total, we know that there are 4
outputs.
• To calculate the input number, the router sends the input number
with the 7th bit set.
0x80 = “1000 0000” input 0
0x81 = “1000 0001” input 1
…
0x8F “1000 1111” input 15
Notes:
When successful, commands #1-4 will acknowledge by sending the
checksum with nibbles swapped & <CR><LF>
e.g. checksum of 0x24 acknowledges with <0x42><CR><LF>
Using RS-232 Control (continued)
