I'm trying to communicate with a Ingenico Eftpos machine. I'm having
trouble getting the checksum of a string of hex charaters

Below works

// String to write into the port
StringToWrite is string = HexaToBuffer("0249034A")
02 Start of text
49 The letter I to initialize eftpost machine (Login)
03 End Of Text
4A the checksum of 02 49 03




But I need to work the checksum out in my code not just hard code it as
I need to send different types of request all with diff checksums.

Has anyone done this? and could pass the code to me or point me in the
right direction.

PS I'm new to WinDev

Thanks in advance...

Mark