Assembly Program for Ramp/Staircase Waveform (8085/8086 example) - 5.1.2 | Experiment No. 6: Analog-to-Digital (A/D) and Digital-to-Analog (D/A) Conversion Interfacing | Microcontroller Lab
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5.1.2 - Assembly Program for Ramp/Staircase Waveform (8085/8086 example)

Practice

Interactive Audio Lesson

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Introduction to DAC Interfacing

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0:00
Teacher
Teacher

Today, we’re going to explore how a Digital-to-Analog Converter, or DAC, works and how it can interface with a microprocessor to produce analog signals. Can anyone tell me what a DAC does?

Student 1
Student 1

A DAC converts digital signals into analog values!

Teacher
Teacher

Correct! The DAC takes binary inputs and translates them into continuous analog outputs. This is crucial because microprocessors operate using digital data, but we often need to interface with the analog world. Remember this key concept: DAC = Digital to Analog. Can anyone think of applications for DACs?

Student 2
Student 2

They are used in audio devices, right? To convert digital audio files into sound.

Teacher
Teacher

Exactly, great point! Now, let’s move on to how we can implement a program to generate a staircase waveform with a DAC.

Teacher
Teacher

In our assembly program, we'll incrementally send values to the DAC by using the OUT instruction. Let's look at the code snippet together.

Assembly Code Breakdown

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0:00
Teacher
Teacher

Here is the example code for our ramp waveform generation. Can someone read the first line?

Student 3
Student 3

'ORG 0000H' initializes the program starting at memory address 0000H.

Teacher
Teacher

Perfect! Then we set the accumulator to zero with 'MVI A, 00H.' What does this accomplish?

Student 4
Student 4

It initializes the accumulator with the starting digital value of zero.

Teacher
Teacher

Exactly! After this, we enter a loop where we'll continuously output this value to the DAC with 'OUT 40H.'

Teacher
Teacher

What happens with 'INR A'?

Student 1
Student 1

'INR A' increments the accumulator, preparing the next digital output.

Teacher
Teacher

Right again! And our loop continues until A overflows, where we can observe the staircase waveform. Can anyone summarize what we should expect to see on the oscilloscope after running this program?

Student 2
Student 2

A staircase waveform that increases in steps corresponding to the digital values we send!

Execution and Observations

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0:00
Teacher
Teacher

Now that we understand the code, how will we observe the resulting waveform?

Student 3
Student 3

We connect the DAC's output to an oscilloscope, right?

Teacher
Teacher

Exactly! By running the program, we should see a ramping staircase shape observed on the oscilloscope. Can someone recall how we should measure the peak voltage and step size?

Student 4
Student 4

We measure the maximum height of the stairs for peak voltage and the vertical distance between steps for step size.

Teacher
Teacher

Good job! Finally, let’s recap what we learned today about generating analog waveforms using assembly programming for our DAC. Can someone summarize the steps from beginning to end?

Student 1
Student 1

First, we connect the DAC, then write and run the assembly program, and finally observe the waveform on the oscilloscope!

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section outlines the assembly program used to generate a ramp or staircase waveform using the 8085/8086 microprocessor and a Digital-to-Analog Converter (DAC).

Standard

The section describes the assembly program that generates a staircase waveform by incrementally sending digital values to a DAC. It includes an example code snippet for the 8085 microprocessor and explains the procedure for observing the resulting waveform.

Detailed

Assembly Program for Ramp/Staircase Waveform

The assembly program for generating a ramp or staircase waveform is executed using the 8085 or 8086 microprocessor in conjunction with a Digital-to-Analog Converter (DAC). The fundamental goal of this program is to produce a linearly increasing analog voltage by sending a series of incremental digital values to the DAC. This waveform can be visualized using an oscilloscope.

Key Elements Covered in This Section

  • Interfacing DAC: The section provides a clear methodology on how the DAC is interfaced with the microprocessor using specific port addresses for communication.
  • Assembly Code Explanation: The detailed example of assembly code demonstrates the initialization and looping required to continuously output increasing values to the DAC.
  • Execution and Observation: An outline of how to connect the DAC to an oscilloscope for waveform observation effectively demonstrates practical application. The peak voltage and step sizes are highlighted to verify the DAC's performance, linking it directly to theoretical parameters.

In conclusion, this section emphasizes the relationship between digital inputs provided to a microprocessor and the resultant analog outputs through practical programming.

Audio Book

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Introduction to the DAC0808 Interfacing

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Interfacing Schematic for DAC0808:

  • Connect DAC0808 D0-D7 to the microprocessor's D0-D7 data bus.
  • Connect the V_REF+ pin to +5V (or desired reference voltage).
  • Connect the V_REF- pin to ground.
  • Connect the Power Supply pins: VCC to +5V, VEE to -5V (or ground if using single supply mode).
  • Connect I_OUT to an external current-to-voltage converter circuit using an op-amp (e.g., LM741) and a feedback resistor. A common configuration uses a 5k Ohm feedback resistor with V_REF = +5V.

Detailed Explanation

In this section, we focus on how to connect the DAC0808 digital-to-analog converter to a microprocessor. The first step is to connect the digital input pins (D0-D7) of the DAC to the corresponding data bus of the microprocessor. The V_REF+ pin, which sets the maximum output voltage, should be connected to +5V, and V_REF- is grounded, establishing the reference level for the analog output.

We also need to supply power to the DAC by connecting VCC to +5V and VEE to -5V, unless using a single supply, in which case VEE can go to ground. The current output from the DAC (I_OUT) needs to be converted to a voltage using an operational amplifier (like LM741) which is done by using a feedback resistor, often sized at 5k Ohm, with V_REF set to +5V, to get a meaningful output voltage.

Examples & Analogies

Think of the DAC0808 as a water tap that controls the flow of water (or voltage) based on the digital signal it receives. Each increment in the digital input can be compared to turning the tap slightly to let out more water, which relates to increasing voltage levels in our circuit.

Assembly Code for Waveform Generation

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Assembly Program:

  • Aim: Generate a linearly increasing analog voltage output (staircase waveform) by sending incremental digital values to the DAC.
  • Microprocessor: 8085 (example)
  • Port Address: Assume DAC is interfaced at Port 40H.
; 8085 Assembly Code for Ramp Waveform Generation
ORG 0000H
MVI A, 00H ; Initialize Accumulator with 0
LOOP:
OUT 40H ; Output A to DAC (Port 40H)
; DAC converts this digital value to an analog voltage
INR A ; Increment A
JNZ LOOP ; Repeat until A overflows (goes from FFH to 00H)
HLT ; Halt

Detailed Explanation

This assembly code is an instruction set that allows us to create a staircase waveform using the DAC. First, we set the initial value of the accumulator (the register A) to 0 using MVI A, 00H, indicating that the output will start at 0 volts. The LOOP label indicates the start of a repeating section.

Inside the loop, OUT 40H sends the current value in the accumulator to the DAC at port address 40H, where the DAC converts this digital value into an analog output. The instruction INR A increments the value in the accumulator by 1 to prepare for the next analog value. The JNZ LOOP keeps the program looping until the accumulator overflows back to 0 from 255 (FFH in hexadecimal), at which point the program halts with HLT.

Examples & Analogies

You can think of this process as filling a bucket with water where each increment of a digital value fills the bucket just a little more until it reaches the top. When it overflows, the filling process starts again, mimicking the staircase nature of the output waveform.

Execution and Observation of the Generated Waveform

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Execution and Observation:

  • Connect the DAC's analog output to an oscilloscope.
  • Run the assembly program.
  • Observe the oscilloscope display. A staircase waveform should be visible, starting from 0V and increasing incrementally up to the full-scale voltage, then resetting to 0V.
  • Measure the step size and peak voltage to verify DAC operation.

Detailed Explanation

After completing the assembly program, we need to connect the DAC output to an oscilloscope to visualize the waveform being produced. Once we run our program, the output displayed on the oscilloscope should show a staircase-like pattern that starts at 0V, increases steadily in steps, and once it reaches the maximum output capable by the DAC, it resets back to 0V and repeats.

In practice, we would measure the peak voltage to ensure it aligns with our expected maximum output, typically around the reference voltage set at the beginning. Additionally, examining the step size (the voltage increment for each digital count) provides feedback on the DAC's resolution and performance.

Examples & Analogies

Picture this like a staircase where each step represents a voltage increment. The oscilloscope is like a camera capturing the scene of someone walking up these steps – you can see the person (the voltage) rising at each stage until they reach the top before coming back down to the ground level.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • DAC Function: A DAC converts digital information into analog signals.

  • Assembly Programming: Necessary for instructing the microprocessor to output specific values.

  • Ramp Waveform Properties: Important characteristics of the staircase waveform, including step size and peak voltage.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Example of a DAC0808 generating a staircase waveform with a maximum voltage of 5V.

  • Using a potentiometer to adjust the input voltage and observing its effect on the output waveform.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • DAC takes the digital track, outputs voltage with a knack!

📖 Fascinating Stories

  • Imagine a staircase where each step up represents a digital value increasing; that's how a DAC outputs ramp signals!

🧠 Other Memory Gems

  • DAS: Digital to Analog Step – remembering the DAC's purpose!

🎯 Super Acronyms

DAC

  • Digital Analog Conversion - a journey from bits to waves!

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: DAC

    Definition:

    Digital-to-Analog Converter that translates digital signals into analog voltages or currents.

  • Term: Assembly Code

    Definition:

    A low-level programming language that is closely related to machine code and facilitates programming for hardware interfaces.

  • Term: Ramp Waveform

    Definition:

    A waveform that increases steadily and linearly, creating a staircase appearance when plotted.

  • Term: Microprocessor

    Definition:

    An integrated circuit that contains the functions of a central processing unit (CPU) of a computer.

  • Term: OUT Instruction

    Definition:

    An assembly command used to send data to peripheral devices such as DACs.

  • Term: Accumulator

    Definition:

    A register in a microprocessor used to store intermediate results of arithmetic and logic operations.