Assign Memory Addresses and Create Memory Map
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Introduction to Memory Interfacing
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Today, we'll discuss memory interfacing with the 8085 microprocessor. Can anyone tell me what memory interfacing is?
Isn't it how the microprocessor connects to RAM and ROM?
Exactly! Memory interfacing allows the microprocessor to read from and write to memory. What do you think is the significance of the address bus?
It helps identify specific memory locations, right?
Correct! The 8085 uses a 16-bit address bus. That allows it to access 65,536 memory locations! Remember the acronym 'RAM - Read And Modify' to help you recall that RAM is used for temporary data storage.
What about ROM? What role does it play?
Great question! ROM is non-volatile and holds firmware. It's important for booting the system. Letβs summarize: memory interfacing is crucial, the address bus identifies memory locations, and RAM is temporary while ROM is permanent.
Creating a Memory Map
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Now, let's talk about creating a memory map. Why do you think it's necessary?
To ensure memory addresses donβt overlap?
Exactly! A memory map shows how memory addresses are allocated for different devices. For example, how many address lines do you think a 2 KB ROM would need?
Eleven address lines, since 2 KB is 2048 bytes.
Right! And a 4 KB RAM requires twelve address lines. Letβs visualize this: if ROM starts at 0000H and occupies the first 2 KB, what is its ending address?
It would be 07FFH.
Perfect! The RAM starts where the ROM ends to avoid overlap. This careful planning is essential for functional memory operation.
Address Decoding Logic
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Next, letβs discuss address decoding. Can anyone explain what it is?
Itβs used to select the right memory chip based on the incoming address.
Exactly! We use logic gates or decoders like the 74LS138 to implement this. Why do we need decoding?
To prevent multiple chips from responding to the same address!
Great insight! So, if A11 to A15 are all 0, what does that indicate for the ROM?
That it should be selected.
Exactly! Decoding ensures that we only activate the right chip. Always remember: decode for clarity.
Read/Write Operations
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Weβve covered memory mapping and address decoding. Now, letβs dive into read/write operations. Who can tell me how the 8085 performs a memory read?
It places the address on the address bus and activates overlineRD, right?
Exactly! The selected memory chip then puts its data on the data bus. And for writing data, what changes?
The 8085 places the data on the data bus and activates overlineWR.
Correct! An easy way to remember this: 'Read > Address First, Write > Data First'. Letβs recap: reading transfers data from memory to 8085 while writing does the reverse.
Practical Application with Assembly Language
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Finally, letβs look at how we apply these concepts using assembly language. What is the goal of the assembly code we write?
To move data in and out of memory effectively!
Exactly! Letβs write a code snippet to store a value in RAM. Can anyone provide the starting operation?
ORG 0000H for the program start!
Perfect! And how do we specify the address to write to?
Using LXI to load the address into HL register.
Exactly right! Remember these steps as you execute on the trainer kit. Practice makes perfect!
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section provides an overview of memory interfacing with the 8085 microprocessor, detailing concepts like memory mapping, address decoding, and procedures for executing read/write operations with RAM and ROM.
Detailed
Detailed Summary
The section on assigning memory addresses and creating a memory map is crucial for understanding how the 8085 microprocessor interacts with memory elements such as RAM and ROM. The 8085's 16-bit address bus allows it to access up to 64 KB of memory, making effective memory management vital.
To create a memory map, relevant parameters such as the size of the ROM and RAM must be established first. For instance, a 2 KB ROM can be addressed using 11 address lines (A0-A10), while a 4 KB RAM uses 12 address lines (A0-A11). The section further elaborates on the assignment of memory addresses, starting from a defined base for both ROM and RAM, ensuring that no overlaps occur. This leads to the generation of unique chip select signals through address decoding logic.
Decoding is performed using various logic gates or dedicated decoder ICs, such as the 74LS138. The section also outlines how to perform read/write cycles β describing the specific control signals activated by the 8085 during these operations. Students are equipped with practical assembly code examples to interact with memory effectively, further reinforced through the verification of each operation on an 8085 trainer kit. Understanding these principles lays the groundwork for further exploration and troubleshooting in microprocessor-based systems.
Audio Book
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Memory Address Assignment for ROM
Chapter 1 of 4
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Chapter Content
β ROM: Assign starting address 0000H.
β Ending Address = 0000H+2048β1=07FFH.
β Address Range: 0000Hβ07FFH.
Detailed Explanation
In this chunk, we are assigning a starting address for the ROM memory. The starting address is 0000H, which is the first address in the memory space. To find the ending address, we add the size of the ROM, which is 2048 bytes (2KB), to the starting address and subtract one. This gives us an ending address of 07FFH. Therefore, the complete address range for the ROM is from 0000H to 07FFH.
Examples & Analogies
Think of a library where the books have to be organized in a way that each book (like each memory location) has a specific shelf number (the address). In our case, the ROM is like a special section of the library starting from shelf 0 (address 0000H) and going all the way to shelf 7FFH, storing important reference books that you won't throw away.
Memory Address Assignment for RAM
Chapter 2 of 4
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Chapter Content
β RAM: Assign starting address 2000H (leaving a gap for other potential devices/expansion).
β Ending Address = 2000H+4096β1=2FFFH.
β Address Range: 2000Hβ2FFFH.
Detailed Explanation
For the RAM, we assign it a starting address of 2000H. This keeps it separate from the ROM and leaves a gap for any potential devices that may need to be added later. To calculate the ending address, we take the starting address, add the size of the RAM, which is 4096 bytes (4KB), and subtract one. This results in an ending address of 2FFFH. Thus, the RAM occupies the addresses from 2000H to 2FFFH.
Examples & Analogies
Continuing our library analogy, imagine you have a second section for borrowing books (the RAM), starting from shelf 2000H. You've reserved some space for potential future sections in between, so your borrowing section starts here and goes up to shelf 2FFFH, helping avoid confusion with the books in your reference section.
Memory Map Table Creation
Chapter 3 of 4
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Chapter Content
- Complete Memory Map Table:
Memory Size Starting Ending Address Decoding
Device Address Address Lines Used Address Lines
by Chip (for Chip Select)
ROM 2KB 0000H 07FFH A0-A10 A11, A12, A13,
A14, A15 (all
must be 0)
RAM 4KB 2000H 2FFFH A0-A11 A12, A13, A14,
A15 (A12=1,
others=0)
Detailed Explanation
After assigning addresses, we create a memory map table that summarizes the memory configuration. For each memory device, we list its size, starting and ending addresses, and the lines used for address decoding. For ROM, which occupies 2KB, the address range is from 0000H to 07FFH, using address lines A0 to A10. For RAM, using 4KB, the range is from 2000H to 2FFFH, utilizing address lines A0 to A11. This table helps visualize how memory is allocated and how it can be accessed.
Examples & Analogies
This is like creating a directory for your library: you have a section for reference books (ROM) and a separate section for books that can be borrowed (RAM). The table acts like a map, showing where everything is, how many shelves each section has, and the rules on who can access what (which helps avoid any mix-ups).
Address Decoding Logic
Chapter 4 of 4
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Chapter Content
- Design Address Decoding Logic and Interfacing Schematic:
β Common Connections:
β 8085 A0-A10 to ROM A0-A10.
β 8085 A0-A11 to RAM A0-A11.
β 8085 D0-D7 to ROM D0-D7 and RAM D0-D7.
β 8085 overlineRD to ROM overlineOE and RAM overlineOE.
β 8085 overlineWR to RAM overlineWE (ROM does not have overlineWE).
Detailed Explanation
In this chunk, we establish the connections between the 8085 microprocessor and the memory devices (ROM and RAM). Address lines A0 to A10 from the 8085 are connected to the corresponding lines on ROM, while A0 to A11 connect to RAM. The data lines D0 to D7 are connected to both memory types for reading and writing data. Control signals like overlineRD and overlineWR are also connected, with RAM being able to write with overlineWR while ROM only reads data.
Examples & Analogies
Consider this as setting up connections in our library where the librarian (8085) needs to reach different sections (ROM and RAM). The librarian has specific request forms (address lines) to access different bookshelves (data lines), and only certain requests allow them to take out books (control signals) from each section. This ensures that the librarian gets the right book when they ask.
Key Concepts
-
Memory Map: A graphical representation of how memory addresses are allocated in a system.
-
Address Decoding: A technique to select a particular memory device based on address lines.
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Memory Read/Write Operations: Procedures carried out by the microprocessor to transfer data to and from memory.
Examples & Applications
A 2KB ROM requires 11 address lines, covering addresses 0000H to 07FFH.
The RAM may start from 2000H to prevent overlap with ROM, occupying addresses 2000H to 2FFFH.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
In memory mapping, don't overlap,
Stories
Imagine a librarian organizing books on shelves. Each shelf has a label (address) and a decoding system ensures that when a request for a book is made, it goes directly to the right shelf, avoiding confusion and ensuring efficiency.
Memory Tools
To remember the order of memory types: 'Randy (RAM), Reads (ROM) Red (Read Only), Write (RAM can also write)'
Acronyms
Address Bus
'A-Bus
Flash Cards
Glossary
- Memory Mapping
The process of assigning distinct memory addresses to different hardware components to avoid conflicts.
- Address Bus
A collection of wires that carry memory addresses from the microprocessor to memory chips.
- Data Bus
A collection of wires used to transfer data between the microprocessor and memory.
- Control Signals
Signals generated by the microprocessor to control memory read and write operations.
- Chip Select
A signal that enables access to a specific chip among multiple memory devices.
- Address Decoding
The technique used to determine which memory device is to be selected for a particular address.
Reference links
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