*********************************************************************************************
* Switch-Debouncer IC Creates A Long-Period Timer *
* Phill Leyva, Maxim Integrated Products, Sunnyvale, CA *
* *
* ==> Project Description <== *
* Switch debouncer used as a long period external timer, allowing the microcontroller to reduce power * * *
* consumption by entering a sleep mode. *
* *
* Total Elapsed Time = Count_T x Timer_period where *
* Count_T = Number of external Timer periods *
* Timer_period (s) = (63k x C1 x (-ln(1 - VT/VCC)) + 0.1s) *
* VT = MAX6817 threshold voltage *
* VCC = MAX6817 VCC voltage *
* *
* ICs utilized in project: *
* Motorola MC68HC705J1A Microcontroller *
* MAXIM MAX6817 ESD Protected CMOS Switch Debouncer *
* Fairchild FDV303N N-Channel Digital FET *
* *
* ==> Program Description *
* The Start section initializes the registers and I/O. The remaining code consists of the Main Program, the *
* subroutines Input, Control, and Output, and interrupt subroutine IRQ_ISR. *
* *
* After power up, subroutine Input obtains current data from input Port A and stores it in the Input Data *
* Table (IN_Port). Subroutine Control transfers this IN_Port data to the Output Data Table (OUT_Port), *
* and accepts the user's control logic algorithm. Subroutine Output transfers the new output data *
* (OUT_Port) to Output Port B. *
* *
* Finally, the Main Program calls the Interrupt subroutine (IRQ_ISR) when U1 has timed out for 1 period, *
* and adds 1 to the counter. Count T specifies the number of timer periods before waking up the *
* microcontroller. The Main program controls the flow of the program, and enters a low-power wait state *
* when the input and output have been updated. *
* *
***********************************************************************************
* Register Equates *
***********************************************************************************
PORTA equ $00 ; Port A byte address
PORTB equ $01 ; Port B byte address
DDRA equ $04 ; Port A Data Direction Register
DDRB equ $05 ; Port B Data Direction Register
TSCR equ $08 ; Timer Status and Control Register
TCR equ $09 ; Timer-Counter Register
ISCR equ $0A ; Interrupt Status and Control Register
PDRA equ $10 ; Pull-Down Register Port A
PDRB equ $11 ; Pull-Down Register Port B
EPROG equ $18 ; EPROM Programming Control Register
COPR equ $7F0 ; COP Reset Register
MOR equ $7F1 ; Mask Option Register
***********************************************************************************
* I/O Port Register Equates *
***********************************************************************************
* Port A Data Register (PORTA Address = $00)
PA0 equ 0 ; Port A bit 0, Input Bit
PA1 equ 1 ; Port A bit 1, Input Bit
PA2 equ 2 ; Port A bit 2, Input Bit
PA3 equ 3 ; Port A bit 3, Input Bit
PA4 equ 4 ; Port A bit 4, Input Bit
PA5 equ 5 ; Port A bit 5, Input Bit
PA6 equ 6 ; Port A bit 6, Input Bit
PA7 equ 7 ; Port A bit 7, Input Bit
* Port B Data Register (PORTB Address = $01)
PB0 equ 0 ; Port B bit 0, Output Bit
PB1 equ 1 ; Port B bit 1, Output Bit
PB2 equ 2 ; Port B bit 2, Output Bit
PB3 equ 3 ; Port B bit 3, Output Bit
PB4 equ 4 ; Port B bit 4, Output Bit
PB5 equ 5 ; Port B bit 5, Output Bit
* Timer Status and Control Register (TSCR Address = $08)
RT0 equ 0 ; Real-Time Interrupt Rate Select bit 0
RT1 equ 1 ; Real-Time Interrupt Rate Select bit 1
RTIFR equ 2 ; Real-Time Interrupt Flag Reset
TOFR equ 3 ; Timer Overflow Flag Reset
RTIE equ 4 ; Real-Time Interrupt Enable
TOIE equ 5 ; Timer Overflow Interrupt Enable
RTIF equ 6 ; Real-Time Interrupt Flag
TOF equ 7 ; Timer Overflow Flag
***********************************************************************************
* Memory Equates *
***********************************************************************************
RAM equ $00C0 ; Start of on Chip Static RAM
EPROM equ $0300 ; Start of on Chip ROM/EPROM
Vectors equ $07F8 ; Start of Reset/Interrupt Vectors
Timer_INT equ $07F8 ; Timer Vector
IRQ_INT equ $07FA ; External Hardware Interrupt Vector
SWI_INT equ $07FC ; Software Interrupt Vector
RESET equ $07FE ; Reset Vector
***********************************************************************************
* Program Equates *
***********************************************************************************
Count_T equ $04 ; Number of external Timer periods desired
; Total elapsed time=Count_T x Timer_period
***********************************************************************************
* RAM Variables *
***********************************************************************************
org RAM ; Start of Static RAM address
IN_Port rmb 1 ; Byte Wide, Input Data Table
OUT_Port rmb 1 ; Byte Wide, Output Data Table
Count rmb 1 ; External Timer pulse counter
***********************************************************************************
* Program I/O Initialization *
* Default for PORTA is as INPUT Port *
* PortA Pins 7 6 5 4 3 2 1 0 *
* Function In In In In In In In In *
* Default for PORTB is as OUTPUT Port *
* PortB Pins 5 4 3 2 1 0 *
* Function Out Out Out Out Out Out *
***********************************************************************************
org EPROM
Start: sei ; Mask OFF Hardware Interrupt
clra ; Clear Accumulator
sta PORTA ; Blank data for registers
sta DDRA ; Set Port A Byte Wide Inputs
sta IN_Port ; Clear Input Data Table
sta OUT_Port ; Clear Output Data Table
sta Count ; Clear external timer counter
sta PORTB ; Initialize Port B MCU-Latches
lda #$FF ;
sta DDRB ; Set Port B as Output Port
lda #$0F ;
sta TSCR ; Disable Timer Interrupts
clrx ; Clear Index Registor
clra ; Clear Accumulator
sta COPR ; Reset Watchdog timer
jsr Input ; Get initial Input Port A data
jsr Control ; Manipulate Data Tables
jsr Output ; Send out initial Output Port B data
cli ; Mask ON Hardware Interrupts, enable
; external timer interrupts
***********************************************************************************
* Main Program *
***********************************************************************************
Main: wait ; Enter power saving mode until awaken by
; by timer (IRQ\) or system reset (RESET\)
lda #Count_T ; Number of external Timer periods desired
sbc Count ; Subtract (Count_T - Count)
bls Next ; Test if accumulator is zero or negative
jmp Main ; Counter not done
Next: jsr Input ; Counter done, get new Input Port A data
jsr Control ; Transfer data tables and other user tasks
jsr Output ; Send out new Output Port B data
jmp Main ; Do another loop through Main
***********************************************************************************
* Input Port A Update Subroutine *
***********************************************************************************
Input: lda PORTA ; Read new Input Port A data
sta IN_Port ; Update Input Data Table
rts ; Return from Subroutine
***********************************************************************************
* Control Logic Update Subroutine *
***********************************************************************************
Control: nop ; USER to remove "nop"s and insert CONTROL<<*
nop ; LOGIC routine here <<**********************
lda IN_Port ; Read new Input table data
sta OUT_Port ; Update Output table
rts ; Return from Subroutine
***********************************************************************************
* Output Port B Update Subroutine *
***********************************************************************************
Output: lda OUT_Port ;
sta PORTB ; Send new data to Output Port B
rts ; Return from Subroutine
***********************************************************************************
* Interrupt Service Routine *
* External Timer (MAX6817) has pulsed once *
***********************************************************************************
IRQ_ISR: inc Count ; Add 1 to counter
rti ; Done with Interrupt Routine
*****************************************************************************
* Timer Interrupt Service Routine *
*****************************************************************************
TIMER_ISR: nop ; Future User Timer Routine
rti ; Done with Interrupt Routine
*****************************************************************************
* Software Interrupt Service Routine *
*****************************************************************************
SWI_ISR: nop ; Future User Sofware Routine
rti ; Done with Interrupt Routine
*****************************************************************************
* RESET and Interrupt Vectors *
*****************************************************************************
org Vectors
org Timer_INT
fdb TIMER_ISR
org IRQ_INT
fdb IRQ_ISR
org SWI_INT
fdb SWI_ISR
org RESET
fdb Start
*****************************************************************************
* MOR Vectors *
*****************************************************************************
org MOR
db $20 ; Set MOR Register Options, no Watchdog
rti ; Done with Interrupt Routine
*****************************************************************************
* Timer Interrupt Service Routine *
*****************************************************************************
TIMER_ISR: nop ; Future User Timer Routine
rti ; Done with Interrupt Routine
*****************************************************************************
* Software Interrupt Service Routine *
*****************************************************************************
SWI_ISR: nop ; Future User Sofware Routine
rti ; Done with Interrupt Routine
*****************************************************************************
* RESET and Interrupt Vectors *
*****************************************************************************
org Vectors
org Timer_INT
fdb TIMER_ISR
org IRQ_INT
fdb IRQ_ISR
org SWI_INT
fdb SWI_ISR
org RESET
fdb Start
*****************************************************************************
* MOR Vectors *
*****************************************************************************
org MOR
db $20 ; Set MOR Register Options, no Watchdog