First of all ....
Say sorry to all lovely ladies,, incloud the thousand year old FAIRY. 純文法錯誤 ... 老童言無忌囉, 我很愛女生的.
I hope, my wife won't kick on my skinny butt and let me sleep on cold lonely sofa at night....hahaha...

哈.. 哈.. 看懂啦 !!! Happy ..
我沒用過 rlf 這麼個指令 ....
以為是把 Index 內容向左移一位, 而跟 carry 無關,
原來 rlf 是 Rotate left through carry .
我還真笨耶...

Oh~~~~~

You called her 'it'!
How dare you are!
You have offended all women in the world !!!
(雖然是實話, 但別忘了丹麥佬因為說 自認的實話 而被穆斯林追殺).

Hahaha ...

哇...哇.... 看起來簡單, 原來是如此煩雜 .
謝謝您詳細的解釋...
笨鴨我需要時間好好消化一下...

By the way ,the thousand year old fairy is yours.
You keep it and I'm not going to touch it.
I would rather stay in 忠孝信義商圈 with 台北美媚...
hahaha ....

Hi! Duck,

That was Billie Chic on Mars.
I was on the moon with the fairy (and you were by my side). Remenber?! ^_^.

Full name of 'rlf f,d' instruction is 'rotate left f through carry'.
After rlf operation, content in carry flag will be in the LSBit of register f.

Imagine that if content of 'Index' is '0000 0000', 'SDA' is 'HI' and it is cloned to carry flag.
Content of __ 'Index' ___ 'Carry Flag'
'_________ 0000 0000____ 1

after 'rlf Index' is excuted,
Content of __ 'Index' ___ 'Carry Flag'
'_________ 0000 0001____ 0

Content of carry flag is now rotated into 'Index' as its LSB and the MSB of 'Index' is now in carry flag.

Let's take another example,
If serial data byte sent to SDA is '1010 1010'.
Whole strory of 'Read_byte' will be,
Content of __ 'Index' ___ 'Carry Flag'
'_________ 0000 0000____ 1 ; New SDA value cloned
'_________ 0000 0001____ 0 ; 'rlf Index' excuted.

'_________ 0000 0001____ 0 ; New SDA value cloned
'_________ 0000 0010____ 0 ; 'rlf Index' excuted.

'_________ 0000 0010____ 1 ; New SDA value cloned
'_________ 0000 0101____ 0 ; 'rlf Index' excuted.

'_________ 0000 0101____ 0 ; New SDA value cloned
'_________ 0000 1010____ 0 ; 'rlf Index' excuted.

'_________ 0000 1010____ 1 ; New SDA value cloned
'_________ 0001 0101____ 0 ; 'rlf Index' excuted.

'_________ 0001 0101____ 0 ; New SDA value cloned
'_________ 0010 1010____ 0 ; 'rlf Index' excuted.

'_________ 0010 1010____ 1 ; New SDA value cloned
'_________ 0101 0101____ 0 ; 'rlf Index' excuted.

'_________ 0101 0101____ 0 ; New SDA value cloned
'_________ 1010 1010____ 0 ; 'rlf Index' excuted.

Serial data byte on SDA now is in 'Index'.
Is it amazing?!

Carry flag is not for the purpose of testing, but for bit transitting.
Did you catch what I'm trying to tell?

Dear Wu..
哈... 了解,謝謝啦!!
But... clr carry flag and set carry flag 在此程式中好像是沒有關聯, 也許是其他程式會掣偵測吧 !Am I right??

Hi! Dear Duck,

For some private reasons, I disapeared for a period.
Did you back to TWN for Thanksgiving?
IOU one meal. You may get it anytime you will be in TWN again.

In your 'R_loop':
Carry flag was firstly reset to 'LO' and then 'SDA' is tested.
If 'SDA' is 'HI', then set carry flag (to 'HI').
It implies that
"if 'SDA' is 'LO', carry flag stays as 'LO'".

The 'SDA' state is now cloned to carry flag, isn't it?
After 'rlf' 8 times, one complete byte sent to 'SDA' is now in 'Index'.

OK La!
Look forward to hearing from you again.

Dear All ....
看到一個12c508 副程式 可以將一位元組資料由24Cxx內讀出,
在由FSR- Index 傳回.. 程式 如下....

Read_byte
movlw 11111101b ; SDA=input
tris GPIO ;
bsf SDA ;
movlw 08 ;
movwf temp ;
R_loop
bsf SCL ; SCL=H
clrc ; clr carry.
btfsc SDA ;
setc ; set carry
rlf Index ;
bcf SCL ;
decfsz temp ;
goto R_loop
retlw
不懂的是 clr carry 和 set carry 在做些甚麼呢 ???