Xilica XD Series - Manual (Page 3)

The Checksum is calculated from <01> to the character before the checksum, which should be <1F>.
The formula used is:
byte i, nChksum;
byte nTx[256];
for (i = 0, nChecksum = 0; i++) nChecksum += nTx[i]; // Add all hex number before the checksum
//
nTx is the buffer holding all transmit data
nChecksum %= 0x60; // Modulo of <60> (Remainder when divided by <60>)
nChecksum += 0x20; // Add <20> to become readable ascii
So is the value of nChecksum.
The process byte is always <1F>. It tells the device to process the information (Command, Device, I/O, Channel, Aux
commands and values) before it.