Time delay period

Projects Programming
1

Can anyone tell me what time delay is represented in the following code for a couple of delays, written for Arduino Nano so I assume 16Mhz clk?
delay_us
LDI R21, 255
15: DEC R21
BRNE_15
RET
;-----------------------------------
delay_ms:
LDI R21, 255
17: LDI R22, 255
18: LDI R23, 20
19: DEC R23
BRNE 19
DEC R22
BRNE 18
DEC R21
BRNE 17
RET
**;=======================================================

2

I do not know the number of clock cycles for every command (maybe the ATmega328P datasheet has it) but most are "one cycle" at 62.5ns per cycle...

;--------------- ; cycles -------------
    LDI R21, 255 ; 1
15: DEC R21      ; (1 + 255) 
    BRNE_15      ; 2 (1 if not branching)
    RET          ; 1
;-----------------------------------
delay_ms:
    LDI R21, 255 ; 1
17: LDI R22, 255 ; 1
18: LDI R23, 20  ; 1
19: DEC R23      ; (1 + 20) *
    BRNE 19      ; 2 (1 if not branching)
    DEC R22      ; (1 + 255) *
    BRNE 18      ; 2 (1 if not branching)
    DEC R21      ; (1 + 255) = 1,376,256
    BRNE 17      ; 2 (1 if not branching)
    RET          ; 1
;-----------------------------------

ATmega328P_assembly_instructions.pdf (65.9 KB)

3

Homework assignment?

4

Need to pgm for different clk rate.

5

What about 16MHz/65.2ns needs to be reprogrammed?

6

Hello tripoli519214

Tell us the project goal to do this modifications.

1 Like
7

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