I am working on support for the Retevis RT23. I've captured a serial download. I've even successfully downloaded a "factory" image from the radio. But after looking at the data blocks, it appears that there is a checksum at the end of each block of data.

In this block the checksum is 0xf0

[11/03/2017 16:23:00] Read data (COM2) 57 0e 10 10 ff ff ff ff ff ff ff ff ff ff ff ff W...ÿÿÿÿÿÿÿÿÿÿÿÿ ff ff ff ff f0 ÿÿÿÿð

In this block the checksum is 0x83

[11/03/2017 16:23:00] Read data (COM2) 57 0e 40 10 89 08 ff ff ff ff ff ff ff ff ff ff W.@.‰.ÿÿÿÿÿÿÿÿÿÿ ff ff ff ff 83 ÿÿÿÿƒ

In this block the checksum is 0xf5

[11/03/2017 16:23:00] Read data (COM2) 57 0e 50 10 00 00 55 16 00 00 35 46 ff ff ff ff W.P...U...5Fÿÿÿÿ 00 00 14 ff f5 ...ÿõ

And this block the checksum is 0x00

[11/03/2017 16:23:00] Read data (COM2) 57 0d 90 10 00 00 00 00 00 00 00 00 00 00 00 00 W. ............. 00 00 00 00 00 .....

To be honest, I don't have a clue how to figure out a formula to calculate this checksum. Any help with this would be greatly appreciated.

I have attached the complete serial port capture. Thanks in advance.

Jim KC9HI