; ************************************************************************************ ; * SerialIO.asm - full duplex software UART ; * -- serial input/output based on timer interrupt ; * ; * Alan Probandt - Portland Oregon USA alan_probandt@yahoo.com ; * ; * Code designed for the Atmel AVR Tiny11/12, works OK with Tiny26 or 90S1200 ; * ; * version 1.00 Sept 30, 2004 ; * ; * 3.579MHz color burst crystal operation -- change 'Clock' variable value for other crystal values ; * ; * ; * Use Terminal or other unkerned font ; * in text editor to format this file correctly, set tab stop to 8 ; ; ; Atmel AVR Tiny11 ; RESET/ PIN 1 | VCC PIN 8 +5V ; 3.579MHz Xtal PIN 2 PB3 | PB2 PIN 7 Soft UART Transmit Out ; color burst PIN 3 PB4 | PB1 PIN 6 ; PIN 4 Gnd | PB0 PIN 5 Soft UART Receive In ; ; ******************************************************************************************** ; How the program works ; ; ; The Tiny11 timer overflows every half BAUD period (16 microseconds for MIDI - 53 uSec for 9600 baud) ; The code does not interrupt on the falling edge of the input start bit like hardware UARTs do. ; The interrupt routine checks if the MIDI input pin is low. This will indicate the start bit ; of a serial-in byte has occurred. The timer interval is one half of a BAUD to always catch ; an input start bit. ; When an input start bit is seen, the In_Active and In_Phase flag are set. ; The Input counter value set at 9 by reset or the previous serial input activity. ; After start bit detection on the input pin, data is shifted in on every second timer interrupt. ; ; New data from the UART is ready when the NewInputDataReady flag in InControl register is set. ; ; Serial output begins when the main code puts the data byte into the TxData register ; and sets the Out_Active flag in the OutControl register. Before loading new data to be sent, ; wait until the Out_Active flag is clear. This means the previous tranmit is finished. ; ; Resources Used: ; four registers - static data between interrupts, plus one scratch register ; Timer0, 2 I/O pins ; 88 program words, not including demo in main program ; ; ******************************************************************************************** .nolist .include "Tn11def.inc" .list .equ Clock = 3579545 ; television color burst frequency - cheap common crystal value .equ TimerPreScaler = 1 ; clock divisor value, not AVR control register setting .equ BaudRate = 38400 .equ TimerInterval = BaudRate * TimerPreScaler .equ ReloadCycleLatency = 6 ; # of cycles between Overflow and TCNT0 having reloaded count value .equ HalfBAUDTime = Clock/(TimerInterval * 2) .equ TimerReloadValue = (256-(HalfBAUDTime)) + ReloadCycleLatency ; software UART definitions .equ SoftUARTout = PortB .equ SoftUARTin = PinB .equ SoftUARTDDR = DDRB .equ TxPin = 2 ; PB2 - Tiny11 pin 7 .equ RxPin = 0 ; PB0 - Tiny11 pin 5 ;********************************************************************************************* ; Register definitions ; ; lower registers ; r0 is used for reading table data in program memory using the LPM instruction and ZH-ZL register pair ; upper registers .def temp = r16 ; scratch register .def irqtemp = r17 ; interrupt's scratch register .def InControl = r18 ; bits 0-3 are shift counter bits 7-4 are status flags ; Serial input control register flag values .equ In_Active = 7 .equ In_Phase = 6 ; Flag indicates whether to read RxPin data on current Timer IRQ .equ NewInputDataReady = 5 ; set when a new byte is ready to be read from the RxData register .def OutControl = r19 ; bits 0-3 are shift counter bits 7-4 are status flags ; Serial output control register flag values .equ Out_Active = 7 .equ Out_Phase = 6 ; Flag indicates whether to change TxPin data on current Timer IRQ .def TxData = r20 .def RxData = r21 .def quickloop = r1 .def bigloop = r2 ;********************************************************************************************* .cseg .org $0000 rjmp reset ; Reset handler $000 ;***************************************************** ; ; Timer Overflow Interrupt Code ; ;***************************************************** .org OVF0addr ; $003 Timer 0 overflow handler ; Since interrupt vectors after this one aren't used, it's OK to put the timer IRQ ; routine here and save two clock cycles of IRQ latency by using no RJMP instruction. ; 16 cycles total per IRQ if no software UART activity. OVT0: ldi irqtemp, TimerReloadValue out TCNT0, irqtemp ; restore the timer count to one half baud period ; | ; sbr# bittest for condition /?\ flow chart ; rjmp -condition false | |n ; rjmp -condition true y| | sbrc InControl, In_Active ; check for processing an input byte first. rjmp ReadActive sbic SoftUARTin, RxPin ; check for new start bit rjmp CheckIfOutActive ; no input activity, so check now for output NewInputStart: sbr InControl, (1 << In_Active) | (1 << In_Phase) cbr InControl, (1 << NewInputDataReady) rjmp CheckIfOutActive ; input complete, now check output ReadActive: sbrc InControl, In_Phase ; if clear, read the current data on the input pin now rjmp InPhaseSet ; if set, send the next bit of transmitted data on next interrupt rjmp ReadInputData InPhaseSet: cbr InControl, (1 << In_Phase) ; this phase is inactive, so clear flag rjmp CheckIfOutActive ; no input activity, so check now for output ReadInputData: mov irqtemp, InControl ; read counter inside of the InControl reg andi irqtemp, 0b00001111 ; isolate counter from control flags tst irqtemp breq In_Done cpi irqtemp,1 breq In_StBit sec sbis SoftUARTin, RxPin clc NewInputBit: ror RxData In_StBit: sbr InControl, (1 << In_Phase) ; skip input activity on next timer interrupt DecCntr: mov irqtemp, InControl ; decrement counter inside of the InControl reg andi irqtemp, 0b00001111 ; isolate counter from control flags dec irqtemp andi InControl, 0b11110000 ; erase old counter value from InControl register or InControl, irqtemp ; put new counter value into InControl register rjmp CheckIfOutActive ; input complete, now check output In_Done: ldi InControl, 9 ; initialize input counter and Active flag (cleared) sbr InControl, (1 << In_Phase) | (1 << NewInputDataReady) rjmp CheckIfOutActive ; input complete, now check output ; @@@@@@@@ serial output section CheckIfOutActive: sbrs OutControl, Out_Active LeaveTimerInterrupt: ; single exit point for interrupt routine reti ; no Serial data being processed, so leave timer interrupt sbrc OutControl, Out_Phase ; if clear, send the next bit of transmitted data now rjmp OutPhaseSet ; if set, send the next bit of transmitted data on next interrupt rjmp DoOutput OutPhaseSet: cbr OutControl, (1 << Out_Phase) ; this phase is inactive, so clear flag rjmp LeaveTimerInterrupt ; no output activity, so leave interrupt handler DoOutput: mov irqtemp, OutControl ; check which bit of TxData is being transmitted now andi irqtemp, 0b00001111 ; by reading the counter section of the control register tst irqtemp breq Out_Done cpi irqtemp, 10 breq Out_DoStart cpi irqtemp,1 breq Out_DoStop lsr TxData brcc LowOutputData sbi SoftUARTout, TxPin rjmp DecOutCnt LowOutputData: cbi SoftUARTout, TxPin DecOutCnt: mov irqtemp, OutControl ; decrement counter inside of the OutControl reg andi irqtemp, 0b00001111 ; isolate counter from control flags dec irqtemp andi OutControl, 0b11110000 ; erase old counter value from OutControl register or OutControl, irqtemp ; put new counter value into OutControl register SetOutPhase: sbr OutControl, (1 << Out_Phase) ; skip output activity on next timer interrupt rjmp LeaveTimerInterrupt Out_DoStart: cbi SoftUARTout, TxPin rjmp DecOutCnt Out_DoStop: sbi SoftUARTout, TxPin rjmp DecOutCnt Out_Done: ldi OutControl, 10 ; initialize output counter and Out_Active flag (cleared) rjmp SetOutPhase ;;==================================================== ;******************************************************** ; ; Main Code ; ;******************************************************** RESET: ldi temp, TimerReloadValue ; load one half BAUD period into timer register out TCNT0, temp ldi temp, (1 << TOV0) ; unmask Timer interrupt and reset Overflow Flag out TIMSK, temp ldi temp, ( (0<