7219 shifting

george miyagi · 2005-06-20 07:55

hi
got the 7219 working!!! but am having a funny problem where the data is shifting (sometimes) one column to the right.
Is there a bit of buggy code, or could it be a power problem.
Here's the code, adapted from the Nuts n Volts article:


' ----[noparse][[/noparse] I/O Definitions ]-------------------------------------------------
Clock  CON 0   ' shift clock to MAX7219 
DPin  CON 1   ' shift data to MAX7219 
Load  CON 2   '  
 

 
' ----[noparse][[/noparse] Constants ]------------------------------------------------------- 
' 
Decode  CON $09   ' bcd decode 
'Decode  CON $00  
Intensity CON $0A   ' brightness 
Scan  CON $0B  ' scan (column) limit 
ShutDn  CON $0C   ' shutdown (1 = on) 
Test  CON $0F   ' display test mode 
Yes  CON 1 
No  CON 0 
 
 
' ----[noparse][[/noparse] Variables ]------------------------------------------------------- 
' 
index  VAR NIB   ' loop counter 
idxOdd  VAR index.BIT0  ' is index odd? (1 = yes) 
d7219  VAR BYTE   ' data for MAX7219 
char  VAR BYTE   ' character ee address 
col  VAR NIB   ' column value 
row  VAR NIB   ' row value 
eeAddr1  VAR    BYTE   ' ee pointer 
eeAddr2  VAR BYTE 
vScroll  VAR WORD   ' scrolling data buffer 

' ----[noparse][[/noparse] EEPROM Data ]----------------------------------------------------- 
' 
 
Char_B      DATA %11111111  ' xxxxxxx 
          DATA %10111111  ' x..x..x 
          DATA %10111111  ' x..x..x 
         DATA %11111111  ' x..x..x 
          DATA %11111111  ' .xx.xx. 
        DATA %11111111  ' .xx.xx. 
        DATA %11111111  ' .xx.xx. 
        DATA %11111111  ' .xx.xx. 
 DATA 0 
 
Char_S      DATA %01010101  ' .x..xx. 
          DATA %10101011  ' x..x..x 
          DATA %01010101  ' x..x..x 
          DATA %10101011  ' x..x..x 
          DATA %01010101  ' .xx..x.
        DATA %10101011  ' .xx.xx. 
        DATA %01010101  ' .xx.xx. 
        DATA %10101011  ' .xx.xx.  
 ' DATA 0 
 
Char_2      DATA %10101010  ' x..x..x 
          DATA %11010101  ' x..x..x 
          DATA %10101010  ' x..x..x 
          DATA %11010101  ' .xx..x.
        DATA %10101010  ' .xx.xx. 
        DATA %11010101  ' .xx.xx. 
        DATA %10101010  ' .xx.xx.  
        DATA %11010101  ' .x..xx. 

Char_3      DATA %00011000  ' x..x..x 
          DATA %00111100  ' x..x..x 
          DATA %01111110  ' x..x..x 
          DATA %11011011  ' .xx..x.
        DATA %11111111  ' .xx.xx. 
        DATA %01011010  ' .xx.xx. 
        DATA %10000001  ' .xx.xx.  
        DATA %01000010  ' .x..xx. 
 


 
' ----[noparse][[/noparse] Initialization ]-------------------------------------------------- 
' 
Initialize: 
DIRL = %111     ' clock, data and load pins 
 
FOR index = 0 TO 5 ' six addresses & values (from 0 to 5)              
LOOKUP index,[noparse][[/noparse]Scan,7,Intensity,7,Shutdn,1],d7219 ' those values stored in VAR d7219 one by one 
SHIFTOUT Dpin,Clock,MSBFIRST,[noparse][[/noparse]d7219] ' ... and sent to 7219 when pulsed
IF idxOdd = No THEN NoLoad ' not a clue what this does
PULSOUT Load,3 ' pulsed here (sent to 7219)

NoLoad:
'DEBUG ? d7219
NEXT

' ----[noparse][[/noparse] Main Code ]------------------------------------------------------- 
' 
Main: 
 
Flash_Characters:    ' on screen, one at a time 
  FOR char = 0 TO 3 
    LOOKUP char,[noparse][[/noparse]Char_B,Char_S,Char_2,Char_3],eeAddr1 
    GOSUB ShowChar 
    PAUSE 2000 
  NEXT 

 GOTO Main
 
 
' ----[noparse][[/noparse] Subroutines ]----------------------------------------------------- 
' 
ShowChar: 
  FOR col = 1 TO 8    ' character is 8 columns wide 
    READ (eeAddr1 + col - 1),d7219  ' read column data fromEEPROM 
    SHIFTOUT Dpin,Clock,MSBFIRST,[noparse][[/noparse]col,d7219] 
PULSOUT Load,3 
PAUSE 50
  NEXT 


  RETURN

also, what is the theory around cascading/daisy chaining the 7219s. how do you get date onto say a second 7219

thanks
george

Dave Paton · 2005-06-20 13:37

Regarding the loading of the chips, take another look at page 13 of the 7219/7221 datasheet:

http://pdfserv.maxim-ic.com/en/ds/MAX7219-MAX7221.pdf

I think all you need to do is shiftout the right number of bits and then kick the load9/CS) line. Think of them as serially cascaded shift registers.

I don't see anything overtly wrong with the code, but I don't have time to do more than glance at it right now. Hopefully someone else can give it a more in-depth look.

My $0.02

-dave

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7219 shifting

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