8-bit MicrocontrollersのトピックRe: Help me to understand lines of code

Help me to understand lines of code

Tianshu — Fri, 08 Oct 2010 14:43:44 GMT

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

Re: Help me to understand lines of code

bigmac — Thu, 29 Oct 2020 08:57:16 GMT

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

Re: Help me to understand lines of code

Tianshu — Sun, 10 Oct 2010 10:14:48 GMT

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

Re: Help me to understand lines of code

bigmac — Sun, 10 Oct 2010 10:20:47 GMT

Hello 刘宇,

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

Regards,

Mac

Re: Help me to understand lines of code

Tianshu — Thu, 29 Oct 2020 08:57:18 GMT

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