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' This Program demonstrates the use of the MAX7219, seven segment decoder driver
' It also incorporates placing of Decimal point.
Device 16F84
' ** Set Xtal Value in MHz **
Declare Xtal = 4 ' Set Xtal Frequency
' ** Declare Pins Used **
Symbol Clk = PORTB.0 ' Data is clocked on rising edge of this pin
Symbol Dta = PORTB.1 ' Bits are shifted out of this pin
Symbol Load = PORTB.2 ' Transfers data to LEDs when Pulsed
' ** Declare Constants **
Symbol Decode_Reg = 9 ' Decode register, a 1 turns on BCD decoding for each digit.
Symbol Lum_Reg = 10 ' Intensity register.
Symbol Scan_Reg = 11 ' Scan-limit register.
Symbol Switch_Reg = 12 ' On/Off Register.
Symbol Test_Reg = 15 ' Test mode register (all digits on, 100% bright)
' Symbol Max_Digit = 5 ' Amount of LED Displays being used.
' ** Declare Variables **
Dim Counts As Word ' Variable used for the Demo Counting routine
Dim Max_Disp As Word ' 16-bit value to be displayed by the MAX7219
Dim Max_Dp As Byte ' Digit number to place Decimal point (0-4)
Dim Register As Byte ' Pointer to the Internal Registers of the MAX7219
Dim R_Val As Byte ' Data placed in Each Register
Dim Digit As Byte ' Position of individual numbers within MAX_Disp (0-3)
Dim Position As Byte ' Position of each LED display (1-4)
' ** Initialise 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 Counts = 1 To 9999 ' Increment Counter
Max_Disp = Counts ' Load Max_Disp with Value of Counter
GoSub Display ' Display the Value of Counter
DelayMS 150 ' Delay, so we can see whats happening
Next ' Close the Loop
For Counts = 9999 To 1 Step -1 ' Decrement Counter
Max_Disp = Counts ' Load Max_Disp with Value of Counter
GoSub Display ' Display the Value of Counter
DelayMS 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 = Dig Max_Disp,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 ' Close the Loop
Return ' Exit from subroutine
' Send a 16-bit word to the MAX7219
Transfer:
SHOut Dta,Clk,msbfirst,[Register,R_Val] ' Shift Out the Register first, then the data
High Load ' The data is now acted upon
DelayUS 2 ' A small delay to ensure correct clocking times
Low Load ' Disable the MAX7219
Return ' Exit from Subroutine