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AN #133 - 90S2313 Alarm Clock Print
90S2313 Alarm Clock

This application note was submitted by Nick Baroni.

This Ap Note describes a time clock switch with individually setable on and off times. It is based on a AT90LS2313 and a surplus nine digit common cathode 7 segment LED display such as those found in older calculators

Design notes:
The hardware is described in figure 1. The heart of the unit is a AT90LS2313 run at 2.4576 MHz. A 74HC595 shift register sinks the cathode current from the display. The LED display has tiny (~3mm high) digits and the segment current is about 1.8 mA, set by the 1.8k anode resistors. Even with all digits in a segment on, the resulting 12mA is within the capabilities of the 595.

The cathode of digit 1 is connected to PortD.6 of the 2313. The 595's shift register and latch clocks are tied together. This has the effect of delaying the output and the data input by one clock cycle. Advantage of this is taken in the code.

Three push buttons provide mode and time setting control. The mode switch cycles the control mode between 'run', 'set', 'on' and 'off'.
In the run mode, the slow and fast buttons either turn on or off the load. In the other modes, they increment the time settings. I elected to provide external pull ups rather than enable the internal ones.

An accuracy of 1 second per day implies a frequency accuracy of 1/86400 or 11.6 ppm. Most common CPU crystals are not this accurate and a small trimmer is used on Xtal1 to tune the frequency.

The display is multiplexed. This means that only one of the nine digits is turned on at any time. In order to stop the display flickering, it is important to update each digit quickly enough to allow persistence of vision to make the observer think that all digits are on continuously.

The timer0 overflow interrupt is used to do the display update and count off the time. The crystal used needs to be able to be divided down to exactly one second other wise the clock won't keep accurate time.

The 2457600 Hz clock is divided by 64 to 38400 Hz. Timer 0 is preloaded with 160 every interrupt. This makes timer0 divide by 96 (160 + 96 = 256). The resultant interrupt rate is then 400 Hz.

When the program isn't updating the display, it reads and reacts to the buttons and calculates the display contents.

The following compiler settings were used for this project.
Stacksize=56
Framesize=32
Sstack=8

Figure 1


 



' Clock/timer on 9 digit common cathode muxed display
' N Baroni
' Dec 03

' Port B segment anodes
' PB0 - c
' PB1 - dp
' PB2 - a
' PB3 - e
' PB4 - d
' PB5 - g
' PB6 - b
' PB7 - f

' PD6 Digit 1 cathode
' PD5 - Cathode SR Data
' PD4 - Cathode SR Clk
' PD3 - Switch out
' PD2 - Right button
' PD1 - Middle button
' PD0 - Left button

' Display Digit Cathodes Are On A 595 with Sclk&Rclk connected togther
' So latch outputs are always one step behind what the SR is doing.
' At digit 1, shift one zero into the SR then toggle the clock at sucessive
' digits with srdata high.

$regfile = "2313def.dat"
$crystal = 2457600

Digit1
Alias Portd.6
Ksrdata
Alias Portd.5
Ksrclock
Alias Portd.4
Switchout
Alias Portd.3
Rbut
Alias Pind.2
Mbut
Alias Pind.1
Lbut
Alias Pind.0

Dim Displayram(9) As Byte
Dim Disdigit As Byte
Dim Displaymode As Byte

Dim Dayminutes As Word , Seconds As Byte
' Day is 24*60 = 1440 minutes

Dim Alarmon As Word , Alarmoff As Word

Dim Ticks As Integer
Dim Overflowvalue As Integer

Dim Isupdate As Bit
Dim Itemp As Integer

Declare Sub Time2mem(byval S As Word)
Declare Sub Changemode

Ddrb = &B11111111
Ddrd = &B01111000

'turn off all cathodes
Ksrdata
= 1
For Disdigit = 1 To 9
 
Set Ksrclock
 
Reset Ksrclock
Next
Digit1
= 1
Disdigit
= 1

'init
Displaymode
= 1

' Crystal is 2457600. Prescale of 64 = 38400 at counter input
' preloading with 160 overflows in 96 counts
' 38400/96 = 400
' so have 400 overflows per second.
' One digit per overflow interrupt - 44.44 Hz

Config Timer0 = Timer , Prescale = 64
On Timer0 Muxservice
Enable Timer0
Enable Interrupts
Start Timer0

'Main loop
Do
Debounce Lbut , 0 , Changemode , Sub
If Displaymode = 1 And Mbut = 0 Then
 
Set Switchout
' Displayram(1).1 = 1
' Displayram(2).1 = 1
' Displayram(3).1 = 1
End If
If Displaymode = 1 Then
 
If Rbut = 0 Then Reset Switchout
' Displayram(1).1 = 0
' Displayram(2).1 = 0
' Displayram(3).1 = 0
 Displayram
(1) = 40 'r
 Displayram
(2) = 217 'u
 Displayram
(3) = 205 'n
 
Call Time2mem(dayminutes)
End If

If Displaymode = 2 Then
 
If Isupdate = 0 Then
 
If Mbut = 0 And Rbut = 0 Then
 Dayminutes
= Dayminutes + 60
 
Else
 
If Mbut = 0 Then Dayminutes = Dayminutes + 10
 
If Rbut = 0 Then Dayminutes = Dayminutes + 1
 
End If
 
If Dayminutes >= 1440 Then Dayminutes = 0
 
End If
 Isupdate
= 1
 Displayram
(1) = 181 's
 Displayram
(2) = 188 'e
 Displayram
(3) = 140 't
 
Call Time2mem(dayminutes)
End If

If Displaymode = 3 Then
 
If Isupdate = 0 Then
 
If Mbut = 0 Then Alarmon = Alarmon + 10
 
If Rbut = 0 Then Alarmon = Alarmon + 1
 
If Alarmon >= 1440 Then Alarmon = 0
 
End If
 Isupdate
= 1
 Displayram
(1) = 57 'o
 Displayram
(2) = 41 'n
 Displayram
(3) = 0
 
Call Time2mem(alarmon)
End If

If Displaymode = 4 Then
 
If Isupdate = 0 Then
 
If Mbut = 0 Then Alarmoff = Alarmoff + 10
 
If Rbut = 0 Then Alarmoff = Alarmoff + 1
 
If Alarmoff >= 1440 Then Alarmoff = 0
 
End If
 Isupdate
= 1
 Displayram
(1) = 57 'o
 Displayram
(2) = 172 'f
 Displayram
(3) = 172 'f
 
Call Time2mem(alarmoff)
End If

Loop

'-------------------

Sub Changemode
 
'step through available modes with LH button press.
 
Incr Displaymode
 
If Displaymode = 5 Then Displaymode = 1
End Sub

'-------------------
Sub Time2mem(byval S As Word)
'take time and put in digits 4:9
Local Btemp As Byte , Wtemp As Word , Didx As Byte , Idx As Byte
 
For Idx = 1 To 2
 Wtemp
= S Mod 10
 Btemp
= Lookup(wtemp , Chars)
 Didx
= 2 * Idx
 Didx
= 10 - Didx
 Displayram
(didx) = Btemp '1,2 -> 8,6
 S
= S 10
 Wtemp
= S Mod 6
 Btemp
= Lookup(wtemp , Chars)
 Didx
= 2 * Idx
 Didx
= 9 - Didx
 Displayram
(didx) = Btemp  '1,2 ->7,5
 S
= S 6
 
Next
 Displayram
(6).1 = 1
 Btemp
= Seconds Mod 6
 Btemp
= Lookup(btemp , Squiggle)
 Displayram
(9) = Btemp

End Sub

'--------------------------------------
Muxservice
:
'Timer 0 interrupt routine.
' occurs at 400 Hz. On each interrupt, do clock thing,
' calcuate display contents, display next digit
' Display digit freq = 400/9 = 44.44 Hz

' Do time keeping thing
Tcnt0 = 160
Incr Ticks
If Ticks > 400 Then
 Ticks
= 0
 
Incr Seconds
 
If Seconds = 60 Then
 Seconds
= 0
 
Incr Dayminutes
 
If Dayminutes = 1440 Then
 
' New day
 Dayminutes
= 0
 
End If
 
End If
 
' Check alarm times
 
If Dayminutes = Alarmon Then Set Switchout
 
If Dayminutes = Alarmoff Then Reset Switchout
End If

' Quarter second auto increment
Itemp
= Ticks Mod 100
If Itemp = 50 Then
 Isupdate
= 0
End If

' Push next digit out to display
Portb = 0
If Disdigit = 1 Then
 Digit1
= 0
 Ksrdata
= 0
Else
 Digit1
= 1
 Ksrdata
= 1
End If
 
Set Ksrclock
 
Reset Ksrclock
Portb = Displayram(disdigit)
Incr Disdigit
If Disdigit = 10 Then Disdigit = 1

Return
'End of timer0 interrupt routine


Chars
:
' b76543210
' fbgdeapc
'0: abcdef - 0b11011101 = 221
'1: bc - 0b01000001 = 65
'2: abged - 0b01111100 = 124
'3: abgcd - 0b01110101 = 117
'4: fbgc - 0b11100001 = 225
'5: afgcd - 0b10110101 = 181
'6: cdefg - 0b10111001 = 185
'7: abc - 0b01000101 = 69
'8: abcdefg - 0b11111101 = 253
'9: abcfg - 0b11100101 = 229

Data 221 , 65 , 124 , 117 , 225 , 181 , 185 , 69 , 253 , 229

Squiggle
:
'abcdef
Data 4 , 64 , 1 , 16 , 8 , 128

' b76543210
' fbgdeapc
'A: abcefg - 0b11101101 = 237
'E' adefg -0b10111100 = 188
'F; aefg -0b10101100 = 172
'n: ceafb -0b11001101 = 205
'o: cdeg -0b00111001 = 57
'r: efa - 0b10001100 = 140
's: afgcd - 0b10110101 = 181
't: efa - 0b10001100 = 140
'u' cdefb -0b11011001 = 217

Download source code