4 byte checksum, sum32 algorithm for Epson printers

Question

I'm programming a low level communication with an Epson tm-t88iv thermal printer on a Linux device, which receives only hexadecimal packages. I have read the manual trying to understand how the checksum is built but i can't manage to recreate it.

the manual says that the checksum are 4 bytes representing the 2 bytes sum of all the data in the package sent.

I have currently four working examples I found by listening to a port on a windows computer with a different program. the last 4 hexadecimals are the checksum (03 marks the end of the data and is included in the checksum calculation, according to the manual).

02 AC 00 01 1C 00 00 03 30 30 43 45
02 AC 00 00 1C 80 80 1C 00 00 1C 00 00 1C 03 30 32 32 31
02 AD 07 01 1C 00 00 1C 31 30 03 30 31 35 33
02 AD 00 00 1C 80 80 1C 00 00 1C 00 00 1C 03 30 32 32 32

I have read somewhere that there is a sum32 algorithm but i can't find any example of it or how to program it.

Answer 1

Wow, this is a bad algorithm! If someone else finds himself trying to understand Epson's terrible low-level communication manual, this is how the check-sum is done:

1. The checksum base is 30 30 30 30
2. Sum in hexadecimals all of the data package (for example, 02+89+00+00+1C+80+80+1C+00+01+1C+09+0C+1C+03 = 214)
3. Then separate the result digit by digit, if its a letter add 1 to the value (for example B2 would be 2|1|4).
4. sum it to the checksum base number by number starting from right to left (this would be a checksum of 30 32 31 34).

Note: It works perfectly, but for some reason the examples I posted above don't seem to match so much. They are all the printers response, but slightly after it got a hardware problem and had to be reformatted by technical support, so maybe it got fixed.

I hope it helps somebody somewhere.