Type:
Compiler/Assembler:
This is my first successful attempt to transmit a string with Attiny 804 hardware USART. used the default pins PB2 and ground to transmit from chip to CH340 TTL-USB converter from aliexpress.
The TX pin (PB2) has to made OUTPUT by setting DIR register bit 2 to 1 and the port should be logical 1 or +ve by setting PORT_OUT register bit 2 for transmitting.
Transmits string "My first UART assembly code!" to terminal in windows 7
Code was compiled in ATMEL studio 7
;
; 804USARTasmTX.asm
;
; Created: 3/24/2021 8:09:40 PM
; Author : pappan
;
.include "tn804def.inc"
.equ fclk = 3333333
.equ BAUD = 9600
.equ fBAUD = ((64 * fclk) /(16 * BAUD)+0.5)
.def temp = r16
.macro millis ;macro for calling delay in milli seconds
ldi YL,low(@0)
ldi YH,high(@0)
rcall delayYx1mS
.endm
reset:
lds r16,PORTB_DIR
ori r16,(1<<2)
sts PORTB_DIR,r16 ;set portB PB2 direction as output
lds r16,PORTB_OUT
ori r16,(1<<2)
sts PORTB_OUT,r16 ;set portB PB2 as 1 or +ve
ldi r16,low(fBAUD) ;load low value of fBAUD as calculated in the formula provided above
ldi r17,high(fBAUD) ;load high value of fBAUD as calculated in the formula provided above
sts USART0_BAUD,r16 ;store low fBAUD in BAUD register
sts USART0_BAUD + 1,r17 ;store low fBAUD in BAUD register
ldi r16,USART_TXEN_bm ;0b01000000 ,(1<<6) ,bitmask value to enable USART transmit
sts USART0_CTRLB,r16 ;store TXEN in USART_CTRLB register
rjmp TXUSART ;jump to TXUSART address (main routine)
sendbyte:
lds r16,USART0_STATUS ;copy USART status register to r16
andi r16,USART_DREIF_bm ;(0b00100000) AND with DATA REGISTER EMPTY FLAG bitmask (position5) to check flag status 0= not empty 1= empty
sbrs r16,5 ;skip next instruction if bit 5 is 1 (means flag set for data transmit buffer ready to receive new data )
rjmp sendbyte ;if DREIF = 0 ,bit 5 in r16 is 0 then loop back to sendbyte until DREIF = 1
mov r16,r17 ;copy data to be transmitted from r17 to r16
sts USART0_TXDATAL,r16 ;store r16 in TXDATAL transmit data low register
ret
TXstring:
ldi ZL,low(2*string) ;load low value of string address in low register of Z pointer
ldi ZH,high(2*string) ;load low value of string address in low register of Z pointer
loop:
lpm r17,Z+ ;load from program memory value pointed by Z (first byte/character of the string) and increment address
and r17,r17 ;AND r17 with itself, if null/0x00 or not
breq exit ;if null/0x00 the end of string has reached
rcall sendbyte ;if r17 value not null call sendbyte routine to transmit 1 character
rjmp loop ;jump to loop back through the string until a null is encountered
exit:ret
TXUSART:
rcall TXstring ;call routine to transmit a null terminated string
millis 250 ;delay routine that calls a delay of 250ms
rjmp TXUSART ;infinite loop that keeps transmitting the string
string:
.db "My first UART assembly code!",'\r','\n',0 ; string in " " ,'\r' is carriage return , '\n' is new line
;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;DELAY SUBROUTINES
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; ============================== Time Delay Subroutines =====================
; Name: delayYx1mS
; Purpose: provide a delay of (YH:YL) x 1 mS
; Entry: (YH:YL) = delay data
; Exit: no parameters
; Notes: the 16-bit register provides for a delay of up to 65.535 Seconds
; requires delay1mS
delayYx1mS:
rcall delay1mS ; delay for 1 mS
sbiw YH:YL, 1 ; update the the delay counter
brne delayYx1mS ; counter is not zero
; arrive here when delay counter is zero (total delay period is finished)
ret
; ---------------------------------------------------------------------------
; Name: delayTx1mS
; Purpose: provide a delay of (temp) x 1 mS
; Entry: (temp) = delay data
; Exit: no parameters
; Notes: the 8-bit register provides for a delay of up to 255 mS
; requires delay1mS
delayTx1mS:
rcall delay1mS ; delay for 1 mS
dec temp ; update the delay counter
brne delayTx1mS ; counter is not zero
; arrive here when delay counter is zero (total delay period is finished)
ret
; ---------------------------------------------------------------------------
; Name: delay1mS
; Purpose: provide a delay of 1 mS
; Entry: no parameters
; Exit: no parameters
; Notes: chews up fclk/1000 clock cycles (including the 'call')
delay1mS:
push YL ; [2] preserve registers
push YH ; [2]
ldi YL, low(((fclk/1000)-18)/4) ; [1] delay counter (((fclk/1000)-18)/4)
ldi YH, high(((fclk/1000)-18)/4) ; [1] (((fclk/1000)-18)/4)
delay1mS_01:
sbiw YH:YL, 1 ; [2] update the the delay counter
brne delay1mS_01 ; [2] delay counter is not zero
; arrive here when delay counter is zero
pop YH ; [2] restore registers
pop YL ; [2]
ret ; [4]
; ============================== End of Time Delay Subroutines ============== SCREEN SHOT
