MAX7219 behaves strangely with various PICs and config.
Hello.
Here's sample code I'm using:
Code:
' Program: MAX_CNT.BAS
' *************************************************************
' * For use with EXPERIMENTING WITH THE PICBASIC PRO COMPILER *
' * *
' * This source code may be freely used within your own *
' * programs. However, if it is used for profitable reasons, *
' * please give credit where credit is due. *
' * And make a reference to myself or Rosetta Technologies *
' * *
' * Les. Johnson *
' *************************************************************
'
' This Program demonstrates the use of the MAX7219, seven segment decoder driver
' It also incorporates placing of Decimal point.
' ***********************************************************************
Include "Modedefs.bas"
' ** Set Xtal Value in mHz **
Define OSC 4 ' Set Xtal Frequency
' ** Declare Pins Used **
Clk Var PortB.0 ' Data is clocked on rising edge of this pin
Dta Var PortB.1 ' Bits are shifted out of this pin
Load Var PortB.2 ' Transfers data to LEDs when Pulsed
' ** Declare Constants **
Decode_Reg Con 9 ' Decode register, a 1 turns on BCD decoding for each digit.
Lum_Reg Con 10 ' Intensity register.
Scan_Reg Con 11 ' Scan-limit register.
Switch_Reg Con 12 ' On/Off Register.
Test_Reg Con 15 ' Test mode register (all digits on, 100% bright)
' Max_Digit Con 5 ' Amount of LED Displays being used.
' ** Declare Variables **
Counter Var Word ' Variable used for the Demo Counting routine
Max_Disp Var Word ' 16-bit value to be displayed by the MAX7219
Max_Dp Var Byte ' Digit number to place Decimal point (0-4)
Register Var Byte ' Pointer to the Internal Registers of the MAX7219
R_Val Var Byte ' Data placed in Each Register
Digit Var Byte ' Position of individual numbers within MAX_Disp (0-3)
Position Var Byte ' Position of each LED display (1-4)
' ** INITIALIZE THE MAX7219 **
' Each register address is sent along with its setting data.
' Because the MAX7219 expects to see a packet of 16 bits, then the LOAD pin is pulsed
' Set the scan limit to 3 (4 digits, numbered 0-3)
' Set the Brightness to 5
' BCD decoding to the lower 4 digits
' Switch the display on.
' Turn Off test mode
Register=Scan_Reg ' Point to the Scan Register
R_Val=3 ' send 3, (Four LED Displays 0-3)
Gosub Transfer ' Transfer this 16-bit Word to the MAX7219
Register=Lum_Reg ' Point to the Luminance Register
R_Val=5 ' Send 5, (Value for Brightness)
Gosub Transfer ' Transfer this 16-bit Word to the MAX7219
Register=Decode_Reg ' Point to BCD Decode Register
R_Val=%00011111 ' Decode the first 5 digits
Gosub Transfer ' Transfer this 16-bit Word to the MAX7219
Register=Switch_Reg ' Point to the Switch Register
R_Val=1 ' Set to One, (switches the display ON)
Gosub Transfer ' Transfer this 16-bit Word to the MAX7219
Register=Test_Reg ' Point to the Test Register
R_Val=0 ' Reset to Zero, (turns off Test mode)
Gosub Transfer ' Transfer this 16-bit Word to the MAX7219
' ***** MAIN PROGRAM *****
' This loop increments and then decrements a 16-bit number
' And displays it on Four LED Displays
' The value to be displayed is held in the variable "Max_Disp"
' The Position of the decimal point is held in Max_DP (0-4)
Max_Dp=3 ' Display number for Decimal Point
Again: For Counter=1 to 9999 ' Increment Counter
Max_Disp=Counter ' Load Max_Disp with Value of Counter
Gosub Display ' Display the Value of Counter
Pause 150 ' Delay, so we can see whats happening
Next ' Close the Loop
For Counter=9999 to 1 step -1 ' Decrement Counter
Max_Disp=Counter ' Load Max_Disp with Value of Counter
Gosub Display ' Display the Value of Counter
Pause 150 ' Delay, so we can see whats happening
Next ' Close the Loop
Goto Again ' Do it Indefinately
' ** Subroutines **
' Display the Value held in the Variable "MAX_DISP" on the four LED's
' The value held in "MAX_DP" places the decimal point on that LED (0-3)
' Sending the value 15 blanks the display, this allows Zero suppression
' By setting bit-7 of the value sent to the individual LED displays, the decimal point
' Is illuminated
Display:
Digit=0 ' Start at Digit 0 of Max_Disp Variable
For Position=4 to 1 step -1 ' Start at Farthest Right of Display
Register=Position ' Place Position into Register
R_Val=Max_Disp Dig Digit ' Extract the individual numbers from Max_Disp
If Max_Disp<10 and Position=3 then R_Val=15 ' Zero Suppression for the second digit
If Max_Disp<100 and Position=2 then R_Val=15 ' Zero Suppression for the Third digit
If Max_Disp<1000 and Position=1 then R_Val=15 ' Zero Suppression for the Forth digit
If Max_Disp<10000 and Position=0 then R_Val=15 ' Zero Suppression for the Fifth digit
If Digit=Max_Dp then R_Val.7=1 ' Place the decimal point, held in Max_DP
Gosub Transfer ' Transfer the 16-bit Word to the MAX7219
If Digit>=3 then Digit=0 ' We only need the first four digits
Digit=Digit+1 ' Point to next Digit within Max_Disp
Next Position ' Close the Loop
Return ' Exit from subroutine
' Send a 16-bit word to the MAX7219
Transfer:
Shiftout Dta,Clk,msbfirst,[Register,R_Val] ' Shift Out the Register first, then the data
High Load ' The data is now acted upon
@ Nop
@ Nop ' A small delay to ensure correct clocking times
Low Load ' Disable the MAX7219
Return ' Exit from Subroutine
I have several MAX7219, hooked to different displays, and with different PICs, results are different:
12F683 - no display @ 4mhz, works OK for 3-4 minutes at 8mhz
16F628A - counts to 5 or 8 (depends on MAX chip), then goes off
16F870 - counts fine, however, 2nd digit (from the left) sometimes displays 3, instead of 0. With another MAX chip, screen goes off when displaying 28, and may come back on 33.
Soldering is correct, MAX7219 -s are genuine, obtained from digikey.
Re: MAX7219 behaves strangely with various PICs and config.
Found the reason, but don't know why it happens.
It depends on Max_dp variable.
If it equals 5 or 4, then there's no problem. If 3, 2, or 1, it causes problem. if DP=3, then hangs on 2800 (around), if DP=2, then hangs on 280, if DP=1, then hangs on 8.
What might be the reason?
Re: MAX7219 behaves strangely with various PICs and config.
If anyone interested, the reason for this issue was noisy power supply. Added 100uf capacitor at 7219 power pins - problem gone.
