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Interactive Audio Lesson
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Introduction to ADC0804
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Today we're discussing the ADC0804, a key component for converting analog signals to digital format. Can anyone tell me what that means?
It means it changes a continuous signal into discrete digital values!
Exactly! This is crucial for microprocessors which operate in a digital realm. What are some examples of analog signals we might want to convert?
Temperature or sound are both analog outputs!
Great examples! The ADC0804 can handle 8-bit digital output, which means it can provide 256 different values. This relates to its resolution. Can someone define resolution?
It's the smallest change in analog input that can be detected by the ADC.
That's right! In our example, if we have a 5V reference voltage, the resolution would be 5V divided by 256. This is important for understanding how accurately we can read our analog signals.
To sum up, the ADC0804 is crucial for translating our real-world signals into digital information that our microprocessor can understand.
Connecting the ADC0804 to the Microprocessor
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Now let’s look at how to connect the ADC0804 to a microprocessor. Can anyone describe some important connections?
We need to connect the data pins to the microprocessor’s data bus!
Correct! Additionally, we’re going to need to use control signals properly. Can someone identify some control pins on the ADC0804?
OVERLINE_CS for chip select and OVERLINE_WR for writing data!
Yes, and how do these pins help in the conversion process?
OVERLINE_WR starts the conversion, and OVERLINE_CS selects the chip to communicate with.
Exactly! Establishing these connections correctly ensures our ADC can successfully communicate with the microprocessor, allowing us to read data.
Writing the Assembly Code
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Now we will look at how to write an assembly program for the ADC. Can anyone tell me why we need to send a dummy write to the ADC?
To initiate the conversion process!
Correct again! Here’s a snippet of what that program might look like. Let’s break it down step by step. What does the first line `MVI A, 00H` do?
It loads the accumulator with zero, which is a dummy data value for the ADC.
Exactly! Then we use `OUT 41H` to activate the chip. Why do we need to wait for `INTR` to indicate a conversion is complete?
We need to wait for that before reading back the data to ensure it’s valid!
Great! After confirming the conversion, the code `IN 41H` reads the data back. This process works with the potentiometer for variable voltage input data.
Practical Observations
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Finally, let's discuss what we would observe when we change the input voltage from the potentiometer. What do you think will happen to the digital display?
It should change according to the potentiometer’s setting!
Exactly! If you set it to 2.5V, what would be your expected digital output if the ADC is working correctly?
It should output 80H since that's 128 decimal.
Right on! Each increase in voltage leads to an increase in digital output until it reaches the maximum voltage it can convert. Remember, understanding this process integrates the ADC's functionality with practical applications in electronics.
Introduction & Overview
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Quick Overview
Standard
In this section, students will learn about the ADC0804, its interfacing with the microprocessor, and how to write assembly programs to read analog input and convert it to digital output. The significance of various parameters in ADC conversion, along with examples of interfacing schematics, practical implementations, and expected outcomes, is highlighted.
Detailed
Detailed Summary
In Section 5.2.2, we delve into the assembly programming for an analog-to-digital conversion using the ADC0804 chip with microprocessors like the 8085/8086. The section begins with an exploration of interfacing this ADC with a microprocessor, detailing the necessary connections, including data pins and control signals, to enable the conversion of analog input signals into digital output.
Key Points Covered:
- The section outlines the functionalities of the ADC0804, which is an 8-bit successive approximation ADC. It describes the main components, including its input and output pins, control signals, and the importance of a reference voltage for its operation.
- An effective interfacing schematic is represented that includes connections between the ADC and the microprocessor, demonstrating how to link data, power, and control pins.
- The assembly code is provided, illustrating how to initiate the conversion process and read the converted data. Key parts of the code are annotated to clarify each operation, such as sending a write pulse to start conversion and polling for the completion signal.
- Practical observations of analog values as read from a potentiometer and the corresponding digital output are discussed, reinforcing the principle of ADC conversion and its applications.
The significance of A/D conversion in facilitating digital systems to interact with the analog world is emphasized, showcasing real-world applications in various fields like instrumentation and robotics.
Audio Book
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Interfacing Schematic for ADC0804
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- Interfacing Schematic for ADC0804:
- Connect ADC0804 D0-D7 to the microprocessor's D0-D7 data bus.
- Connect VIN+ to the output of a potentiometer (variable voltage source, 0-5V). Connect VIN- to ground.
- Connect V_REF/2 to +2.5V (for a 0-5V input range, V_REF = 5V. If V_REF is tied to VCC, it sets the max input). Typically, V_REF/2 is connected to VCC/2 or a dedicated 2.5V source. If V_REF is left open, it defaults to VCC.
- Provide a clock source: For internal clock, connect 10k Ohm resistor between CLK R and CLK IN, and 150 pF capacitor between CLK IN and ground.
- Connect Power Supply pins: VCC to +5V, GND to ground.
- Control Signals:
- overlineCS (Chip Select): Connect to I/O address decode output (e.g., Port 41H).
- overlineRD (Read): Connect to microprocessor's overlineRD signal (for I/O read).
- overlineWR (Write): Connect to microprocessor's overlineWR signal (for I/O write).
- INTR (Interrupt): Connect to a status bit that the microprocessor can poll (e.g., a data line from an input port). For simple polling, connect INTR to D0 or D7 of an input port and read that port. Alternatively, use a ready pin if the trainer kit has one.
- Output Display: Connect D0-D7 of the ADC to 8 LEDs with current limiting resistors, or to an LCD module for display.
Detailed Explanation
This chunk explains how to set up and connect the ADC0804 to the microprocessor. The connections are crucial for the ADC to operate correctly:
- Connect the digital output pins (D0-D7) of the ADC to the data bus of the microprocessor. This allows the microprocessor to send commands and receive data.
- The analog input (VIN+) from a potentiometer gives a variable voltage that the ADC will convert.
- The reference voltage (V_REF/2) must be set at 2.5V to ensure that the ADC can handle the full range of 0-5V.
- A clock signal is necessary for the ADC to know when to perform conversions. This can be provided by connecting specific resistors and capacitors for timing.
- Control signals like Chip Select and Read/Write are essential for proper communication between the ADC and the microprocessor. These signals are set for the specific addresses assigned to the ADC, allowing the microprocessor to interact with it as needed.
- Lastly, the output can be displayed on LEDs or an LCD, giving visual feedback based on the ADC's converted values.
Examples & Analogies
Imagine setting up a cashier system in a grocery store. The cashier (microprocessor) needs to communicate with various machines (ADC0804) to process transactions. Just like the cashier needs to know which register to use (data bus connections), what price each item is (analog input from potentiometer), and when to ring up an item (clock signals), the ADC requires specific connections and control signals to operate correctly. The checkout receipt represents the output displayed on the LEDs or LCD, showing customers how much they’ve spent.
Assembly Program for ADC Reading and Display
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- Assembly Program for ADC Reading and Display (8085/8086 example):
- Aim: Read analog voltage from potentiometer, convert to digital, and display on LEDs/LCD.
- Microprocessor: 8085 (example, similar logic for 8086)
- Port Addresses: Assume ADC overlineWR is at Port 41H (dummy write to start conversion), and ADC overlineRD data is at Port 41H (actual read). Assume INTR is connected to bit D7 of Input Port 42H.
- Assembly Code:
; 8085 Assembly Code for ADC Read and Display ORG 0000H ; Initialize (if necessary, for LCD or LED segment drivers) ; For direct LED connection, no special init needed START_CONVERSION: MVI A, 00H ; Dummy data OUT 41H ; Send pulse to ADC WR to start conversion. ; This OUT instruction asserts WR (low) and selects port 41H ; (assuming 41H is decoded for ADC WR) WAIT_FOR_CONVERSION: IN 42H ; Read status of INTR (e.g., from D7 of Port 42H) ANI 80H ; Mask all bits except D7 (INTR connected to D7) JNZ WAIT_FOR_CONVERSION ; Loop until INTR goes low (D7 becomes 0) ; If INTR is active low, it means D7 should be 0. ; So, JNZ means "If D7 is NOT 0, keep waiting" READ_ADC_DATA: IN 41H ; Read digital data from ADC (Port 41H) ; This IN instruction asserts RD (low) and selects port 41H ; (assuming 41H is decoded for ADC RD) MOV B, A ; Store the digital value in B register (for observation/display) ; Optional: Display B on LEDs or LCD ; If LEDs connected directly to data bus for output (e.g., through a latch) ; OUT LED_PORT ; Replace LED_PORT with actual output port for LEDs HLT ; Halt ; Consider a loop to continuously read and display if desired. ; JMP START_CONVERSION ; Uncomment for continuous operation
Detailed Explanation
This section provides specific assembly code meant for the 8085 microprocessor that accomplishes the task of reading from the ADC and displaying the output:
- The program begins by resetting the accumulator with a value (MVI A, 00H).
- It then sends a 'dummy' write signal to Port 41H to initiate the conversion process. This is done through the OUT instruction, signaling the ADC that it should take a reading.
- The program enters a loop where it checks the status of the INTR signal connected to the microprocessor. It will keep checking whether the conversion is complete (INTR goes low). This is where the microprocessor waits for the ADC to finish processing the input.
- Once the conversion is complete, it reads the converted digital value from the ADC through another IN instruction directed at Port 41H.
- The resulting digital output is stored in register B for potential display on LEDs or an LCD, effectively transforming the analog voltage input into a digital representation visible through the output ports.
Examples & Analogies
No real-life example available.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Analog-to-Digital Conversion: The process where an analog signal is converted into a digital value.
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ADC0804 Characteristics: Its ability to handle 8-bit digital representation of analog signals.
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Interfacing Concepts: The importance of proper wiring and use of control signals between ADC and microprocessor.
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Assembly Language Programming: Writing code to manipulate ADC readings effectively.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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Reading a potentiometer input voltage ranging from 0 to 5V using ADC0804 and displaying the digital output on LEDs.
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Using the ADC0804 to convert temperature readings (in volts) from a temperature sensor to digital values for microprocessor processing.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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ADC, see how it ought to be, turning volts into bits, simply and free.
📖 Fascinating Stories
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Once upon a time, a tiny chip named ADC0804 lived in a digital kingdom. It transformed the magical analog signals of the world into numbers that rulers could understand.
🧠 Other Memory Gems
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Remember: Chip Select (CS), Write (WR), Read (RD) – CWR for ADC functionality.
🎯 Super Acronyms
ADC - Analog to Digital Conversion
- A: to D
- we convert for the microcontroller to know!
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: ADC0804
Definition:
An 8-bit Analog-to-Digital Converter used for converting analog inputs into digital outputs.
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Term: Resolution
Definition:
The smallest change in analog input that can be detected by an ADC, determined by V_MAX divided by the number of discrete levels.
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Term: OVERLINE_CS
Definition:
A chip select control pin used to enable the ADC chip.
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Term: OVERLINE_WR
Definition:
A control signal sent to initiate the writing process for the ADC.