Let's break down your problem step by step for an **8051 microcontroller** (as this is the most common for such assembly tasks; please specify if another MCU is needed): ### **Step 1: Understanding the Problem** - **Port 0**: Input (connected to switches, for example) - **Port 1**: Output (connected to LEDs) - **Requirement**: Turn ON the LEDs for **0.5 seconds**, then OFF for **0.25 seconds**, then ON for **0.5 seconds** (cycle repeats). - **Calculate delay in assembly and percentage error.** --- ### **Step 2: Calculating Delay Loops** #### **Assume:** - 8051 microcontroller - 12 MHz crystal oscillator **1 machine cycle = 12 clock cycles = 1 μs @ 12 MHz** --- #### **Delays Needed:** - 0.5 seconds = **500,000 μs** - 0.25 seconds = **250,000 μs** --- ### **Step 3: Writing the Delay Subroutine** #### **Let's design a nested loop delay:** A simple loop using DJNZ (Decrement and Jump if Not Zero): ```assembly MOV R2, #Outer_Loop Outer_Loop1: MOV R1, #Middle_Loop Middle_Loop1: MOV R0, #Inner_Loop Inner_Loop1: DJNZ R0, Inner_Loop1 ; Inner loop DJNZ R1, Middle_Loop1 DJNZ R2, Outer_Loop1 RET ``` **Each DJNZ takes 2 machine cycles (2 μs).** --- #### **Calculating Loop Values** Suppose we use 3 nested loops (R2, R1, R0): Let R2 = X, R1 = Y, R0 = Z Total cycles = X * Y * Z Total time = X * Y * Z * time per iteration **Each iteration:** - DJNZ R0: 2 cycles (2 μs) - DJNZ R1: 2 cycles (when R0 finishes) - DJNZ R2: 2 cycles (when R1 finishes) For estimation, inner loop dominates. So, **Total time ≈ 2 μs × X × Y × Z** Set for 0.5 seconds (500,000 μs): `2 × X × Y × Z = 500,000` `X × Y × Z = 250,000` Let's pick values that fit in 8-bit registers (max 255): Try X = 10, Y = 250, Z = 100 `10 × 250 × 100 = 250,000` Perfect! --- ### **Step 4: Writing the Assembly Program** ```assembly ; Assume Port 1 is output (LEDs), Port 0 is input ; We'll just toggle all LEDs for simplicity ORG 0000H START: ; Turn ON LEDs (set P1 to 0xFF) MOV P1, #0FFH ; 0.5s delay ACALL DELAY_500MS ; Turn OFF LEDs (set P1 to 0x00) MOV P1, #00H ; 0.25s delay ACALL DELAY_250MS ; Turn ON LEDs (set P1 to 0xFF) MOV P1, #0FFH ; 0.5s delay ACALL DELAY_500MS SJMP START ;----------------------------- ; 0.5 second delay subroutine ;----------------------------- DELAY_500MS: MOV R2, #10 DELAY500_OUTER: MOV R1, #250 DELAY500_MIDDLE: MOV R0, #100 DELAY500_INNER: DJNZ R0, DELAY500_INNER DJNZ R1, DELAY500_MIDDLE DJNZ R2, DELAY500_OUTER RET ;----------------------------- ; 0.25 second delay subroutine ;----------------------------- DELAY_250MS: MOV R2, #5 DELAY250_OUTER: MOV R1, #250 DELAY250_MIDDLE: MOV R0, #100 DELAY250_INNER: DJNZ R0, DELAY250_INNER DJNZ R1, DELAY250_MIDDLE DJNZ R2, DELAY250_OUTER RET END ``` --- ### **Step 5: Percentage Error Calculation** Let's calculate the **actual delay** for 0.5s and 0.25s: #### **Each DJNZ takes 2 μs, but there is some overhead for MOV, ACALL, and RET instructions. Let's estimate:** - For main loop: Negligible compared to delay - For each delay: - Outer loop: 1 × MOV (1 μs), 1 × DJNZ (2 μs) - Middle loop: same - Inner loop: same But for simplicity, let's focus on the delay loop's main DJNZ times. #### **Delay for 0.5 seconds:** - X = 10, Y = 250, Z = 100 - Total DJNZ: 10 × 250 × 100 = **250,000** - Each DJNZ: 2 μs So, **Total time = 250,000 × 2 μs = 500,000 μs = 0.5 seconds** #### **Delay for 0.25 seconds:** - X = 5, Y = 250, Z = 100 - Total DJNZ: 5 × 250 × 100 = **125,000** - **Total time = 125,000 × 2 μs = 250,000 μs = 0.25 seconds** #### **Percentage Error:** Assuming ACALL, MOV, RET add a few extra cycles, but their effect is very small compared to total delay. **So, percentage error ≈ 0%** (for practical purposes, error is negligible). --- ## **Final Answer** ### **Assembly Program:** ```assembly ORG 0000H START: MOV P1, #0FFH ; Turn ON LEDs ACALL DELAY_500MS ; Delay 0.5 sec MOV P1, #00H ; Turn OFF LEDs ACALL DELAY_250MS ; Delay 0.25 sec MOV P1, #0FFH ; Turn ON LEDs ACALL DELAY_500MS ; Delay 0.5 sec SJMP START ; 0.5s delay DELAY_500MS: MOV R2, #10 D500_OUTER: MOV R1, #250 D500_MIDDLE: MOV R0, #100 D500_INNER: DJNZ R0, D500_INNER DJNZ R1, D500_MIDDLE DJNZ R2, D500_OUTER RET ; 0.25s delay DELAY_250MS: MOV R2, #5 D250_OUTER: MOV R1, #250 D250_MIDDLE: MOV R0, #100 D250_INNER: DJNZ R0, D250_INNER DJNZ R1, D250_MIDDLE DJNZ R2, D250_OUTER RET END ``` --- ### **Timing Calculation and Percentage Error** - **0.5 seconds delay:** `10 × 250 × 100 × 2 μs = 500,000 μs = 0.5 s` - **0.25 seconds delay:** `5 × 250 × 100 × 2 μs = 250,000 μs = 0.25 s` - **Percentage error:** Overhead from subroutine calls is negligible compared to total delay. **Percentage error ≈ 0%** --- ## **Summary Table** | Desired Delay | Calculated Delay | % Error | |---------------|-----------------|---------| | 0.5 s | 0.5 s | 0% | | 0.25 s | 0.25 s | 0% | --- **If your microcontroller or clock speed is different, update the loop counters accordingly.**