SysEx Checksum

I all,

I would like to find a way to get the correct value for the checksum 3e in this example

F0 50 2C 04 00 11 00 10 20 00 00 01 xx xx 00 SUM F7

the checksum is the summation between (  ) so the sum of 14 bytes before the SUM starting at 50.

xx xx are 8 bit data

F0 ( 50 2C 04 00 11 00 10 20 00 00 01 00 00 00 ) 3e F7

50 + 2C + 04 + 00 + 11 + 00 + 10 + 20 + 00 + 00 + 01 + 00 + 00 + 00 =. 3E

If I use external 8-bit checksum calculator it works perfectly but I can’t find a way in CTRLR, any idea ?

In CTRLR The Zy calculation seems not to be the right solution because I need to include the 12 bytes before the calculation and if I use y with greater value than 9 the result is always 0.

Regards

 

 

Ctrlr