MAX7219 behaves strangely with various PICs and config.
Hello.
Here's sample code I'm using:
I have several MAX7219, hooked to different displays, and with different PICs, results are different: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
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.
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