Part B: Assembly Language Programs and Execution
Interactive Audio Lesson
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Introduction to Memory Interfacing
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Today, we're going to explore how memory interfacing plays a crucial role in the functionality of the 8085 microprocessor. Can anyone tell me what memory interfacing means?
I think it relates to how the microprocessor communicates with RAM and ROM.
Exactly, Student_1! It involves connecting different types of memory chips and ensuring they work seamlessly with the CPU. Memory can be broadly classified into RAM, which is volatile, and ROM, which is non-volatile.
What's the difference between how we use RAM and ROM?
Great question, Student_2! While RAM is used for temporary storage of active data, ROM contains permanent instructions. This means you can read from ROM but not write to it like you do with RAM.
So, how does the 8085 know which memory chip to communicate with?
That's where memory mapping and address decoding come into play! Memory maps define how each chip is connected to specific addresses, and address decoding ensures that only the right chip responds based on the address being accessed.
What happens if the address decoding isn't done correctly?
If it's not done correctly, you could end up with address conflicts where multiple chips might respond to the same address, causing data corruption. It's crucial!
In summary, memory interfacing helps the microprocessor effectively retrieve and store data in the appropriate memory types, and this takes place through well-established mapping and decoding mechanisms.
Assembly Language Programs for Memory Operations
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Now that we understand memory interfacing, let's look at how to implement memory operations through assembly programming. Who remembers the instructions we use to store data in RAM?
Isn't it the MOV instruction?
That's right! For instance, to write data to a specific memory location like 2050H, we first use LXI to load the address and then use MVI to load the data into the accumulator.
What about reading data from memory?
Good observation, Student_2. Retrieving data is just as straightforward. You would again use LXI to load the address and then MOV to transfer that memory content to a register, right?
Can you show us a quick example?
Sure! To write 55H to 2050H, you'd use: `ORG 0000H`, `LXI H, 2050H`, `MVI A, 55H`, `MOV M, A`, `HLT`. This will output 55H to the specified memory address.
And can we confirm that the data wrote correctly?
Absolutely! After executing the program, you can use memory examination functions to check the value at 2050H.
In conclusion, understanding the assembly instructions for loading data and data management practices will dramatically improve our efficiency with memory operations.
Practical Application and Verification
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Now, let's move to the practical exercises where you can see the assembly programs in action! What is the first step after powering on the 8085 trainer kit?
We need to enter the machine code for our programs, starting from address 0000H.
Correct, and itβs essential to verify that the machine codes we entered are accurate. What should we look for?
We should check that all opcodes and operands are correct using the 'Examine Memory' function.
Precisely! Once we verify the code, we can execute the programs. How do we know if a write operation worked?
We can use 'Examine Memory' again to check the content of the designated memory location.
And we can see the registers' contents as well after executing read operations!
Exactly. Observing both memory contents and registers will give us confidence that our operations were successful. Remember, practice will help solidify this knowledge.
In summary, proper procedure from entering code to verifying outputs is crucial in mastering memory interfacing with the 8085.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section covers the principles of memory interfacing with the 8085 microprocessor, detailing assembly language programs for reading and writing data in RAM and ROM. It includes practical procedures, example code, and the significance of address mapping and decoding.
Detailed
Detailed Summary
This section delves into memory interfacing as pertained to the 8085 microprocessor, outlining how it is crucial for effective program and data storage. The 8085 utilizes a 16-bit address bus enabling access to 64KB of memory locations with an 8-bit data bus. Control signals manage data transfers, with specific attention given to the role of RAM and ROM in providing volatile and non-volatile storage respectively. The segment explains memory mapping and the need for address decoding using logic gates or decoder ICs to prevent address overlap.
Key Points of Interest:
- Memory Map and Address Decoding: Establishing a memory map is essential for defining how memory chips are organized within the addressable space of the microprocessor. The importance of address decoding ensures that each memory device responds exclusively to its designated address range.
- Read/Write Operations: The operation cycles for both reading from and writing to memory locations are discussed in detail, backed by assembly code examples like writing data to RAM, reading data from memory, and managing block data transfer between addresses.
- Practical Procedures: The procedures laid out provide students with a hands-on experience of interfacing, and debugging processes, while using an 8085 trainer kit, culminating in a series of exercises that reinforce learning outcomes.
The section concludes with a comprehensive verification process to finalize the operations conducted and reflects on the overall import of memory interfacing in microprocessor-based systems.
Audio Book
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Program to Write Data to Memory (RAM)
Chapter 1 of 3
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Chapter Content
Aim:
Store the data 55H at memory location 2050H.
Assumptions:
Memory location 2050H is within the interfaced RAM.
Assembly Code:
ORG 0000H ; Program starts at 0000H (typical ROM location) LXI H, 2050H ; Load 16-bit address 2050H into HL MVI A, 55H ; Move immediate data 55H into Accumulator A MOV M, A ; Move content of Accumulator (A) to memory location (HL) HLT ; Halt processor
Machine Code (Hexadecimal):
- 21 (LXI H opcode)
- 50 (Lower byte of address)
- 20 (Higher byte of address)
- 3E (MVI A opcode)
- 55 (Immediate data)
- 77 (MOV M, A opcode)
- 76 (HLT opcode)
Detailed Explanation
This program demonstrates how to write data to a RAM memory location. First, we set the program to begin at memory address 0000H, which is where programs typically start. Next, we load the address 2050H into a register pair (HL) using the LXI instruction, allowing us to point to our target memory location. We then move the data value 55H (in hexadecimal) into the accumulator register using the MVI instruction. Finally, we store the contents of the accumulator into the memory location pointed to by HL with the MOV instruction, and the program is halted using the HLT instruction. The machine code section shows the hexadecimal representation of these assembly instructions, which the microprocessor understands directly.
Examples & Analogies
Think of it like writing a note and placing it in a specific drawer (the RAM). You decide where to put the note (address 2050H), write your message (55H) on it, and then slide it into that drawer. Just as you need to remember which drawer you used to find the note later, the program uses the address to know where the data is stored.
Program to Read Data from Memory (RAM/ROM)
Chapter 2 of 3
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Chapter Content
Aim:
Read data from memory location 2050H and store it in register B.
Assumptions:
Memory location 2050H has some data (e.g., from the previous write operation).
Assembly Code:
ORG 0000H LXI H, 2050H ; Load 16-bit address 2050H into HL MOV A, M ; Move content of memory location (HL) to Accumulator (A) MOV B, A ; Move content of Accumulator (A) to Register B HLT
Machine Code (Hexadecimal):
- 21
- 50
- 20
- 7E (MOV A, M opcode)
- 47 (MOV B, A opcode)
- 76
Detailed Explanation
In this program, we demonstrate how to read data from a specific memory address. Similar to the write operation, the program starts at address 0000H. We load the address 2050H into the HL register pair using the LXI instruction. The main difference now is that we use the MOV instruction to retrieve the data residing at the memory location pointed to by HL and place it in the accumulator (A). After loading the data into the accumulator, we transfer this content to register B using another MOV instruction. Finally, the program halts with the HLT instruction. The machine code section provides the hexadecimal equivalents of the assembly instructions, which again are directly executed by the 8085 microprocessor.
Examples & Analogies
Imagine you want to read the note you previously wrote and stored (in the drawer). You go to the same drawer (2050H), open it (load into HL), and take out the note (read the data into the accumulator). After reading it, you decide to write down what you read into your personal notepad (register B). Just as you check the drawer carefully to find the correct note, the program carefully specifies the address to find the data.
Program for Block Transfer of Data
Chapter 3 of 3
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Chapter Content
Aim:
Transfer 5 bytes of data from source addresses 2000Hβ2004H to destination addresses 2100Hβ2104H.
Assumptions:
Both source and destination ranges are within interfaced RAM.
Assembly Code:
ORG 0000H LXI H, 2000H ; Load source starting address into HL LXI D, 2100H ; Load destination starting address into DE MVI C, 05H ; Initialize byte count to 5 in register C LOOP: MOV A, M ; Move data from source (HL) to Accumulator STAX D ; Store Accumulator data to destination (DE) INX H ; Increment HL to next source address INX D ; Increment DE to next destination address DCR C ; Decrement byte count JNZ LOOP ; Jump to LOOP if C is not zero HLT
Machine Code (Hexadecimal):
- 21 (LXI H opcode)
- 00 20 (Source Address)
- 11 (LXI D opcode)
- 00 21 (Destination Address)
- 0E (MVI C opcode)
- 05 (Byte count)
- 7E (MOV A, M opcode)
- 12 (STAX D opcode)
- 23 (INX H opcode)
- 13 (INX D opcode)
- 0D (DCR C opcode)
- C2 (JNZ opcode)
- 09 00 (Address of LOOP label - assuming LOOP is at 0009H)
- 76 (HLT opcode)
Detailed Explanation
This program illustrates how to perform a bulk transfer of data from one block of RAM to another. We start at memory address 0000H and load the starting address of the source data (2000H) into HL while the destination address (2100H) is loaded into DE using the LXI instructions. We also initialize a counter, setting register C to 5, which tells the program how many bytes to transfer. Inside a loop (denoted by the label LOOP), the program retrieves data from the current address pointed by HL into the accumulator (A), then stores this data into the memory address pointed by DE using the STAX instruction. After each transfer, HL and DE are incremented to point to the next bytes, and the counter is decremented. If the counter does not reach zero, the program jumps back to the start of the loop to repeat the process until all 5 bytes are transferred. Lastly, the program halts with HLT. The hexadecimal representation of these instructions is also provided for direct execution on the microprocessor.
Examples & Analogies
Think of this program as a moving team of people shifting boxes from one storage unit to another. Each person (CPU cycle) takes a box (data byte) from the first unit (source 2000H), carries it over (store in accumulator), and places it neatly into the second storage unit (destination 2100H). They count how many boxes theyβve transferred (using register C) and keep going in a loop until theyβve moved all five boxes, ensuring everything is copied correctly.
Key Concepts
-
Assembly Language: A low-level programming language that is closely related to machine code, facilitating direct control over hardware.
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Memory Operations: Essential functions that allow reading from and writing to memory locations in a microprocessor system.
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Data Bus: A set of wires used to transfer data between components of a computer, such as the microprocessor and memory.
Examples & Applications
Writing the value 55H to the address 2050H in RAM using the assembly code: LXI H, 2050H; MVI A, 55H; MOV M, A; HLT.
Reading a byte from the memory address 2050H into register B could be done with: LXI H, 2050H; MOV A, M; MOV B, A; HLT.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
When RAM is near, data's in cheer; ROM saves the lore, but writes no more.
Stories
Once there was a little microprocessor called 8085, who could talk to its friends RAM and ROM. RAM was a restless spirit who never kept memories for long, while ROM was a wise owl, who always remembered the important things forever.
Memory Tools
R.A.M. - Read And Memory: Remember that RAM is for reading and writing, while ROM is strictly for reading.
Acronyms
M.A.P. - Memory Addressing Protocol
This helps us remember the process of addressing and mapping for memory chips.
Flash Cards
Glossary
- Memory Mapping
A graphical or tabular representation of how the memory address space is divided and allocated to different memory chips.
- Address Decoding
The process of determining which memory chip should respond to a specific address by using logic gates.
- RAM (Random Access Memory)
Volatile memory used for temporary storage of data that can be read from and written to.
- ROM (ReadOnly Memory)
Non-volatile memory used for permanent storage of data that can only be read.
- Machine Code
The binary or hexadecimal representation of the assembly instructions that the computer's processor can execute.
- Instruction Set
A collection of machine language instructions that a microprocessor can execute.
Reference links
Supplementary resources to enhance your learning experience.