Binary to BCD conversion

[towlerg]

How about


shift right 4 times (thus losing bottom 4 bits and shifting 0 into top 4 bits)
if 0-9 then add x30
else add x37

mask off the 4 msb's
if 0-9 then add x30
else add x37

so for example 3A
shifted becomes 3
3 + x30 = x33 ASCII for "3"

masked becomes x0A
x0A + x37= x47 ASCII for "F"

[Dave]

Well John, Here is the way I would do it. Assuming all 4, 8 bit counters are connected in series to get 32 bits:

BIGNUM VAR LONG
VALUE VAR BYTE
JUNK VAR BYTE
CHARPOS VAR BYTE
DIGVALUE VAR BYTE

MAIN:
'THIS ASSUMES ALL 4, 8 BIT COUNTERS ARE IN SERIES ON SAME DATA AND CLOCK LINE
'ADJUST DATA AND CLOCK LINE TO YOUR HARDWARE CONFIGURATION

SHIFTIN REGDATAPIN,REGCLKPIN,MSBFIRST,[BIGNUM.BYTE3,BIGNUM.BYTE2,BIGNUM.BYTE1,BIGNUM.BYTE 0]

'32 BIT VALUE IS CLOCKED IN TO LONG VARIABLE

JUNK = 7 'SET DIGIT POINTER FOR 8 DIGITS TOTAL
WHILE JUNK < 255
VALUE = BIGNUM DIG(JUNK) 'VALUE OF DIGIT
CHARPOS = JUNK + 1 'CALCULATED CHARACTER POSITION
low load
shiftout datapin,clockpin,MSBFIRST,[CHARPOS, VALUE] 'DATA SHIFTED TO DISPLAY
high load
JUNK = JUNK - 1 'NEXT DIGIT FROM MSBYTE TO LSBYTE
WEND
pause 1000
goto main

I hope this bit of code will help you.

[cunninghamjohn]

Dave,

Thank you for sharing this, your method does seem a lot simpler. I don't have LONGS available but imagine this could be worked around. I would be interested in having a go with something based on your method and see if there is much difference in the size of the compiled program.

George,

Thanks for your reply. I am a little confused though, does this convert to ASCII rather than BCD?

John

[towlerg]

Thanks for your reply. I am a little confused though, does this convert to ASCII rather than BCD?

I think I misunderstood the question, I thought BCD was a way of expressing a binary value as ASCII characters. So for example a byte would become two ASCII chars, a word 4 ASCII chars etc.

[Dave]

John, If you limit the accumulated value to say 5 digits as in a word (65535 max) then you can use it without LONG's. I use this method to display MPH with 3 decimal places on a terminal thru a serial port by adding:

TX_BYTES(TX_OUTPUT) = $30 + VALUE DIG JUNK 'Turn decimal value into ASCII

[cunninghamjohn]

Dave,

Interesting approach, seems like I got too bogged down in shifting and adding multiple times rather than using the more obvious arithmetic capabilities of PICBASIC.

George,

Thanks for the hint on conversion to ASCII, I'm sure it will come in useful at some stage.
For info, BCD represents the decimal digits 0-9 using a nibble of data. With BCD only the states 0-9 are valid. 0xA to 0xF are forbidden. Its used for seven segment displays, real time clock modules, etc.