7 Segment Displays and MAX7219

[DaveC3]

Bill

I have used these displays for a couple of years and also have made my own displays using the MAX7219. I can tell you they are sensitive at start up you need to ensure you have enough capacitance. For my home brew project I had to add a 100uf cap on the 5 volt lines. Got a lot of strange results without it' I have also included the setup I use with two chips daisey chained.

'###############################################################################    
 ' ====================== MAX7219 SETUP ==========================

MAX_SET_UP:
for a = 0 to 3
    For index = 0 to 7		' Retrieve 8 items from table. 
      LookUp index,[SCAN,7,BRITE,10,DECODE,%11111111,ON_OFF,1],max_dat
      ShiftOut DATA_n,CLK_n,1,[max_dat]
      IF odd = 0  Then noLoad	' If odd is 1, 
      PulsOut LOAD_n,1		' pulse LOAD line.
    NoLoad:				' Else, don't pulse. 
    Next index					' Get next item from table. 
next a
		
return
'' ===================== DISPLAY SUBROUTINE ========================

Max1:

  ShiftOut DATA_n,CLK_n,1,[0,0] '
  ShiftOut DATA_n,CLK_n,1,[seg,dat]	' Send the digit. 
  PulsOut LOAD_n,1				' Load the display. 
  						' Repeat for all 4 digits. 
return						' Done? Return. 

Max2:
    ShiftOut DATA_n,CLK_n,1,[seg,dat]	' Send the digit. 
    ShiftOut DATA_n,CLK_n,1,[0,0]
    PulsOut LOAD_n,1	

return

Good luck

Dave

[Bill Legge]

Dave,

Thanks for the tip, I'll try big caps.

Prices are excellent at Futurlec but the support/documentation is sometimes lacking - still a bargain.

I like your MAX set-up (mine is lots of lines of obvious code!) but cant quite follow it:

1. The set-up generally is of the form [Register,Value]
2. Where Register goes from 0 to F
3. And value is byte sized

4. What is your variable 'a' ?
5. What size is the variable 'Max_dat' ?
6. I can't see how you are writing 'Register' and 'Data' to the MAX?

Regards Bill Legge

[elec_mech]

Bill,

I don't know that I can offer much more help, but it looks like Jerson and Dave have some excellent leads. When you mentioned seven segment displays from Futurelec, it rang a bell. I had a project last year where I needed 3", dual color seven segment displays and I got in touch with the manufacturer in China. They have even more options than what Futurelec offers and you can buy from them directly if you wish - be warned they don't accept credit cards (at least last year), so you have to do a bank transfer, which somehow cost us ~$40 bucks and shipping was about ~$25, but for the quantities you're talking about, it might be worth it. Regardless, they try to be helpful so if you have questions on their units or need a datasheet you can e-mail them and they usually get back to you by the next day. Their website is: http://www.nb-flying.com/.

[DaveC3]

Bill

1. The set-up generally is of the form [Register,Value]
2. Where Register goes from 0 to F
3. And value is byte sized

4. What is your variable 'a' ?
5. What size is the variable 'Max_dat' ?
6. I can't see how you are writing 'Register' and 'Data' to the MAX?

"a" is just a byte used to count, in this case it runs through the setup four times, With two displays I wanted to make sure it was setup correctly. I most likely could have done it with two cycles. ( a little overkill)

Max_Dat is a word

The lookup table has the register followed by the value. The load only happens on an even number so first I shift the "register" then the "value" and load pulse.

Works fine

Here are the variables

DATA_n	var portC.2	' Bits are shifted out this pin # to 7219.
CLK_n 	var portC.0	' Data valid on rising edge of this clock pin.
LOAD_n	var portC.1	' Tells 7219 to transfer data to LEDs.
DECODE 	CON	9	' Control register; a 1 turns on BCD decoding. 
BRITE 	CON	10	' "       "   " intensity register.
SCAN  	CON	11	' "       "   " highest # (0-7) of LED digit.
ON_OFF	CON	12	' "       "   " on/off status of display (0=off).
TEST  	CON	15	' Test mode (all digits/segment on, 100% bright)

max_dat	VAR	WORD	' Word to be sent to MAX7219.

Good luck