8085 Program for an Automatic Lawn Irrigation System

Design an 8085 assembly program that simulates a basic automatic lawn irrigation system. The program should:

Turn ON irrigation only when:
- Manual override is not active
- Soil is dry
- It’s not raining
- It’s not daytime

If manual override is ON, irrigation must always turn on, regardless of other conditions.

🔌 Interface (Ports)

Port (Hex)	Purpose	Input Value Meaning
`00H`	Soil Moisture Sensor	`1 = Moist`, `0 = Dry`
`01H`	Rain Sensor	`1 = Raining`, `0 = Dry`
`02H`	Time of Day	`1 = Daytime`, `0 = Night`
`03H`	Manual Override	`1 = Force ON`, `0 = Auto Mode`
`10H`	Output to Valve	`1 = Irrigation ON`, `0 = OFF`

⚡ TL;DR — Final Working Code

START:
        ; Step 1: Check Manual Override
        IN 03H
        CPI 01H
        JZ MANUAL_ON

        ; Step 2: Check Soil Moisture
        IN 00H
        CPI 01H
        JZ IRRIGATION_OFF

        ; Step 3: Check Rain Sensor
        IN 01H
        CPI 01H
        JZ IRRIGATION_OFF

        ; Step 4: Check Time of Day
        IN 02H
        CPI 01H
        JZ IRRIGATION_OFF

        ; All conditions passed → Irrigation ON
        MVI A, 01H
        OUT 10H
        JMP WAIT_AND_RESTART

MANUAL_ON:
        MVI A, 01H
        OUT 10H
        JMP WAIT_AND_RESTART

IRRIGATION_OFF:
        MVI A, 00H
        OUT 10H
        JMP WAIT_AND_RESTART

WAIT_AND_RESTART:
        MVI C, FFH      ; Simple delay
WAIT:   DCR C
        JNZ WAIT
        JMP START

🧱 Step 1: Control the Irrigation Valve with a Simple Output

Before building decision logic, we first need to define how to turn irrigation ON or OFF from the 8085.

This step introduces the output port connected to the irrigation valve.

📦 Output Interface

Port	Purpose	Accepted Values
`10H`	Irrigation Control Valve	`0 = OFF`, `1 = ON`

We’ll directly send a value to this port to simulate the valve being turned ON or OFF.

🧠 Why Start Here?

It gives us a simple, verifiable action to test
It introduces the concept of output control using the OUT instruction
It lays the groundwork for plugging in more complex logic later

🧾 Code (Manual Valve Control)

MVI A, 01H       ; Load A with 1 to simulate "turn ON"
OUT 10H          ; Send A to port 10H
HLT              ; Stop execution

🧪 Manual Test

Try changing MVI A, 01H to MVI A, 00H to simulate turning OFF the irrigation.

Expected:

Port 10H reflects the ON/OFF signal
Easy to test using I/O monitor in Sim8085

🧱 Step 2: Add Manual Override as Input

Now that we can control the valve through an output port, let’s add manual override as an input condition.

When the override switch is ON (1), irrigation should always turn ON regardless of other sensor inputs.

📦 I/O Interface Update

Port	Purpose	Value `0`	Value `1`
`03H`	Manual Override	Automatic mode	Force irrigation ON
`10H`	Valve Control (OUT)	OFF	ON

🧠 How This Works

We read the override input from port 03H using IN
If the value is 01H, we skip all sensor checks and go straight to turning irrigation ON

This models user-first logic: a manual switch overrides all automation.

🧾 Code Snippet (Manual Override)

IN 03H          ; Read from port 03H (Manual Override)
CPI 01H         ; Compare with 1 (Override ON)
JZ MANUAL_ON    ; If equal, jump to force ON

HLT             ; Temporary end

MANUAL_ON:
MVI A, 01H      ; Force irrigation ON
OUT 10H         ; Send ON signal to valve
HLT

🧪 Manual Test

Try:

03H = 00H  → Should not jump (automation continues)
03H = 01H  → Should jump to MANUAL_ON and turn irrigation ON

🧱 Step 3: Check Soil Moisture Sensor

If the manual override is OFF, we now begin evaluating environmental conditions — starting with the soil moisture sensor.

If the soil is already moist, irrigation is not needed.

📦 I/O Update

Port	Purpose	Value `0`	Value `1`
`00H`	Soil Moisture Input	Dry (needs water)	Moist (skip watering)

🧠 What We’re Doing

Read input from port 00H (soil moisture)
If it’s moist (01H), jump to IRRIGATION_OFF
If dry (00H), continue to the next condition (rain sensor)

🧾 Code Snippet (Soil Moisture Check)

IN 00H          ; Read soil moisture from port 00H
CPI 01H         ; Is soil moist?
JZ IRRIGATION_OFF   ; Yes → skip irrigation

🧪 Manual Test

Try setting:

00H = 01H  → moist → jumps to IRRIGATION_OFF
00H = 00H  → dry   → continues to next condition

🧱 Step 4: Check the Rain Sensor

If the soil is dry and manual override is not active, the next check is the rain sensor.

If it’s currently raining, irrigation should be turned OFF — watering during rain is wasteful.

📦 I/O Summary (Rain Sensor)

Port	Purpose	Value `0`	Value `1`
`01H`	Rain Sensor	No rain (continue)	Raining (skip watering)

🧠 What We’re Doing

Read input from port 01H
If rain is detected (01H), jump to IRRIGATION_OFF
If not raining (00H), proceed to the final check — time of day

This prevents unnecessary watering during active rainfall.

🧾 Code Snippet (Rain Check)

IN 01H          ; Read rain sensor input from port 01H
CPI 01H         ; Is it raining?
JZ IRRIGATION_OFF   ; Yes → turn irrigation OFF

🧪 Manual Test

Try setting:

01H = 01H → raining → jump to IRRIGATION_OFF
01H = 00H → dry → continue to time-of-day check

🧱 Step 5: Check Time of Day Before Irrigation

If the soil is dry, it’s not raining, and manual override is off — the last condition to check is the time of day.

We assume that irrigation should only happen at night (for example, to reduce evaporation).

📦 I/O Summary (Time Sensor)

Port	Purpose	Value `0`	Value `1`
`02H`	Time of Day	Night (continue)	Daytime (skip)

🧠 What We’re Doing

Read port 02H to get time info
If it’s daytime (01H), skip irrigation
If it’s night (00H), proceed to turn it ON

This simulates energy-efficient watering schedules.

🧾 Code Snippet (Time Check)

IN 02H            ; Read time-of-day input
CPI 01H           ; Is it daytime?
JZ IRRIGATION_OFF ; Yes → skip irrigation

If we pass all conditions:

; All checks passed → turn irrigation ON
MVI A, 01H
OUT 10H
HLT

🧪 Final Manual Test Cases

Try these combinations of input:

OVR	SM	RAIN	TIME	Expected Output
1	X	X	X	ON (override)
0	1	X	X	OFF (moist soil)
0	0	1	X	OFF (raining)
0	0	0	1	OFF (daytime)
0	0	0	0	ON (all clear)

🧱 Step 6: Run Continuously in a Monitoring Loop

So far, our program halts after making a single decision. In a real-world irrigation controller, we want it to run forever and re-evaluate conditions regularly.

🧠 Why This Matters

A single check isn’t enough — environment changes with time
Sensors may update inputs (e.g., rain starts after initial dry condition)
Automation means ongoing evaluation, not one-time logic

🔁 Add an Infinite Loop

We add a loop at the end of the program to jump back to the start after each evaluation. To avoid tight-loop issues, we also add a delay to prevent too frequent checks.

🧾 Code Snippet (Looping)

WAIT_AND_RESTART:
        MVI C, FFH     ; Software delay (adjust as needed)
WAIT:   DCR C
        JNZ WAIT
        JMP START      ; Begin sensor checks again

Update all HLT instructions to:

JMP WAIT_AND_RESTART

This makes the program a live system — it continuously watches and reacts.

🧪 Final Behavior

On power-up, the irrigation logic starts running
After each ON/OFF decision, the system waits a little and starts over
You can simulate changing conditions in Sim8085 by updating I/O ports mid-run

📚 Summary

This 8085 assembly program simulates a smart irrigation controller using real-world inputs like moisture, rain, and time. The logic includes:

🧠 Manual override that takes priority over automation
💧 Soil and rain checks to avoid overwatering
☀️ Daytime skipping to conserve water
🔁 Continuous monitoring loop for real-time behavior

Key Takeaways:

IN and OUT are essential for hardware interaction
Multi-condition decision-making can be modeled step-by-step
Infinite loops with delays create realistic control systems

This is a great example of using 8085 assembly for practical automation.