Help me to understand lines of code

[Tianshu]

Hi. I'm a beginner of Freescale 8-Bit MCU. Recent  I read the code below used to erase the EEPROM of DZ60.  I have understood most of code means. But I cannot understand first three line of codes. Should someone like to explain these for me? Thanks!

E_EEPROM:

STA ,X ; H:X中是要擦出的EEPROM段的地址

 NOP

 STA ,X lda #(mFSTAT_FPVIOL + mFSTAT_FACCERR)

sta FSTAT sta 0, x ; H:X中保存着要擦出的EEPROM的地址

lda #mFSTAT_FCBEF

 sta FSTAT

 nop

 CheckDoneEErase:

lda FSTAT

lsla bpl CheckDoneEErase

aix #8

cphx #EEP_END

 blo E_EEPROM

jmp SUCC

[bigmac]

Hello,

I assume that you refer to the following lines -

   STA   ,X   NOP   STA   ,X

This sequence writes the accumulator value directly to the address pointed to by the H:X register, twice.  I am unable to read the Chinese characters in the original comment, but would assume that H:X value represents an address within the flash sector to be erased.

The purpose of writing the value twice escapes me - this does not seem to be a specific requirement of the erase process.

Regards,

Mac

[Tianshu]

Hello, bigmac. Thanks for your replying. I'm sorry to say that my English is not good, and assembly language of HCS08 is little hard to me. Maybe I should remove these three lines of code to see if there is some effect to erase process.

祝好，

        刘宇

[bigmac]

Hello  刘宇,

Do not remove all three lines - at least one write is needed, otherwise the erase will not work.

Regards,

Mac

[Tianshu]

Hello Bigmac

      Thanks for your advise. I guess you mean that STA , X is necessary because we should write any byte to the address in the EEPROM where need to erase.  But  I think the fifth line of code realize the purpose.

sta FSTAT sta 0, x ; H:X中保存着要擦出的EEPROM的地址

      Anyway, let me try to see the effect of removing those code.

      Thanks Mac and a good weekend!

    刘宇