/*
 * ToUpper_USART0.asm
 *
 *  Created: 21/03/2014 15:51:30
 *   Author: Administrador
 */
 .DEF temp = R16  ;temporary register definition
 .EQU lowercase_a = 97  ;ASCII for 'a'
 .EQU lowercase_z = 122 ;ASCII for 'z'
 .EQU TOUPPER = 32 ;to be subtracted from the lowercase to get the uppercase
 .EQU Clock = 16000000 ;processor’s clock frequency, Hz
 .EQU Baud = 9600 ;desired serial port baud rate (bits per second)
 .EQU UBRRvalue = Clock/(Baud*16) -1 ;calculates value to be put in UBRR0H:L


 .CSEG
 .ORG 0x00000 ;reset interrupt vector
      jmp RESET
 .ORG URXCaddr ; 0x00024  -> interrupt vectors for USART0
      jmp USART0_reception_completed

.ORG INT_VECTORS_SIZE ;leave room for IRQ vectors
RESET:
    ;configure USART0
    RCALL init_USART0
    SEI ;enable interrupts globally
Loop:
    ;nothing to do here, just be alive
    NOP
    rjmp Loop
;------- initialize USART0 as 9600baud, asynchronous, 8 data bits, 1 stop bit, no parity -----
init_USART0:
    PUSH R16
    LDI R16, LOW(UBRRvalue)
    STS UBRR0L, R16   ;load the low byte
    LDI R16, HIGH(UBRRvalue)
    STS UBRR0H, R16   ;load the low byte
    ; enable receive and transmit, enable USART0 interrupts (UDR empty, Tx finished, Rx finished)
    LDI R16, (1<<RXEN0)|(1<< TXEN0)|(0<<UDRIE0)|(0<< TXCIE0)|(1<< RXCIE0)
    STS UCSR0B, R16 ;set control register UCSR0B with the corresponding bits
    ; configure USART 0 as asynchronous, set frame format: 8 data bits, 1 stop bit, no parity
    LDI R16, (0<<UMSEL00) |(1<<UCSZ01)|(1<< UCSZ00) |(0<< USBS0)|(0<<UPM01)|(0<< UPM00)
    STS UCSR0C, R16 ;set control register UCSR0C with the corresponding bits
    POP R16
    RET

;----USART0_reception_completed handler --------------------------------------------------
;---
USART0_reception_completed:
    PUSH temp ;this handler routine will be automatically called every 61msec (in this example)
    IN temp, SREG ;Backup SREG. MANDATORY in interrupt handler routines
    PUSH temp

    ;do the desired periodic task here
    LDS temp, UDR0  ;pick up the byte received and do anything with it
    CPI temp,lowercase_a ;'a'
    BRLT USART0_reception_cont ;not a lowercase letter
    CPI temp,lowercase_z+1 ;'z'+1
    BRGE USART0_reception_cont ;not an lowercase letter
    SUBI temp, TOUPPER ;change to Uppercase
    STS UDR0, temp  ;transmits the [modified] byte
 USART0_reception_cont:

    POP temp
    OUT SREG, temp  ;Recover SREG from the previous backup
    POP temp
    RETI ;RETI is MANDATORY when returning from an interrupt handling routine

.EXIT