String & WRITE

[Ron Marcus]

To pack single hex digits into a hex byte, just shift the first digit left four times, then add it to the second digit.

Ron

[BigWumpus]

OK, I just try to make the situation clear...

You receive 8 ASCII-Characters "3", "4", "5", "6", ....
Then you want to pack 2 digits in 1 Byte and write them to the eeprom.

Yust try:
Chars Var byte[8] ;here are the 8 digits
For I=0 to 3 ;generate 4 bytes
;cut off unused bits and pack 2 of them
Dummy=(Chars[I<<1]<<4)|(Chars[(I<<1)+1] & $F)
Write I,Dummy
next I

(Very quick and quite dirty!)

[Darrel Taylor]

Hi BigWumpus,

I know you did it real quick, but I think something's missing.

Dummy=((Chars[I<<1]-"0")<<4)|((Chars[(I<<1)+1]-"0") & $F)

Darrel

[Lotondo]

Thanks for answering, I believe you got me the solution.
I'll try and in case I'm not getting the correct result I'll
come back to you.
Regards
Lotondo

[BigWumpus]

Hi Darrel,

I dont subtract the $30 because
-while shifting it 4 bits to the left, they drop out of the PIC ;-)
-while & $F they where masked out ;-)

try it smart !

[Darrel Taylor]

BigWumpus,

Oh yeah. Your right!

That'll change the way I convert ascii numbers in the future. Thanks.
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[Andrew]

Hello everybody,

Although this topic might be quite old, I would like to "try my luck" to sort out a problem that bothers me for some time.

From the very begining want to state that I am rather a noobie in relation with PIC's and peculiar with its EEPROM operation and actualy this is my first interaction with this forum.

On short, I use DEBUGIN command to capture a 16 characters alphanumeric strings sent from a PC, something like following example:

85D4E88A3B52AA40 (or more corect said "8","5","D","4","E","8","8","A","3","B","5","2","A ","A","4","0").

I do need to WRITE these characters into onchip (PIC16F88) EEPROM, location 0, as pairs consisting of 2 characters in 1 Byte.

At the end of operation the first location of EEPROM memory must looks like this: 85 D4 E8 8A 3B 52 AA 40.
Unfortunately I have ended up with this result: 85 44 58 81 32 52 11 40.

Concernig the pairs of data within the string please note that there are several kind of possible combinations:

- 2 digits (i.e. 85, 40);
- 2 characters (i.e. AA);
- 1 digit and one character, in this order (i.e. 8A, 3B)
- 1 character and one digit, in this order (i.e. D4, E8)

Mention that I have used and adapted BigWumpus' above proposed algorithm.
It works perfectly as long the string contains only digits (0-9).
However, it fails whenever HEX like characters (A,B,C,D,E F) come into picture.

Any help to sort out this problem will be highly appreciated.

Many hanks in advance and wishing you all a Happy and Prosperous New Year !

Best regards,
Andrew

[Andrew]

Although the topic is quite old I am interested to solve a similar problem for which will really appreciate your support / expertise.

On short, I am receiving serially 16 ASCII-Characters, say "3", "B", "5", "A", "7", "F","1", "D", "2", "2", "4", "F","E", "E", "A", "6".

Then I need to pack 2 digits in 1 Byte and write them to the EEPROM. The final result should be: 2B 5A 7F 1D 22 4F EE A6.
Any clue or tip with regard to algorithm or conversion formula will be highly appreciated. Have a happy and prosperous New Year !