Bootloader command set trouble in write memory command set

[DChen.3]

I try use the boot loader command set.

I follow the AN3155 datasheet to use , but i meet a trouble, i can't write bytes over 4 bytes. below is my set step

1. send cmd host -> 31 CE / device-> 79
2. send address+checksum host->08 00 00 00 08 / device->79
3. send number+checksum host->04 00 04 00 20 00 20 / device->79

but if I want to write more byte or one bin file , then device all response 1F(NACK)

example :

host-> 0c 00 04 00 20 a9 8b 00 00 03 8e 00 00 00 00 /device ->1F

send 128 bytes host-> 80 00 04 00 20..............80 00 00 00 00 /device->1F

Could you talk me where is error? thank you

[TDK]

> 04 00 04 00 20 00 20

This writes 5 bytes, not 4.

> 0c 00 04 00 20 a9 8b 00 00 03 8e 00 00 00 00

This writes 13 bytes and the checksum is wrong.

[DChen.3]

Please tell me how to cal the checksum?? and the data string checksum is ?