Binary to BCD conversion

[Dave]

I do believe there is an easier way. One question I have is, How is the original data retrieved or stored ie. LONG or WORD array elements?

[cunninghamjohn]

Dave,

I would be interested to see how you would implement the binary/BCD conversion. The code I posted is my take on the shift and add 3/double dabble routine.

The original data will come from 4 74HC165 shift registers, I will shift in 4 bytes of data and store these as BBIN1...4. The program is part of a frequency counter I am working on. I am 4 using 74HC393 binary counters followed by the shift registers to give a 32 bit count. The PIC will only do the arithmetic and control the MAX7219 display driver. I will be using an external timebase.

I'm sure this isn't the simplest or most elegant way to implement a frequency counter, but I will learn more doing it this way. My first thought is that I may be able to reduce the number of 393/165 chips and count the number of overflows during the timing period to reduce chip count.

I could use 74HC390 to avoid having to do the binary/BCD conversion but this would need more chips due to the redundancy of bits in BCD

Regards,
John

[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