Part A: Memory Map Design and Interfacing Schematic
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Understanding Memory Mapping
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Today, we will learn about memory mapping. Can anyone tell me what a memory map is?
Is it a way to show how memory is organized within the microprocessor?
Exactly! A memory map outlines how the microprocessor's memory space is divided among different components like RAM and ROM. Remember, it helps prevent overlapping and ensures efficient access.
How do we know what sizes to assign to each memory chip?
Great question! The size of memory chips is derived from their specifications. For instance, if we have a 2KB ROM and a 4KB RAM, we need to calculate the address lines required for each.
Can you remind us how to calculate the address lines?
Sure! We use the formula logβ(N), where N is the size in bytes. It's a handy tool to determine how many unique addresses a memory chip can handle.
Does this mean that a 2KB chip requires 11 address lines?
Correct! Well done! Each memory type has specific identifier requirements, which are vital to ensure no address conflicts arise. Todayβs lesson highlights the foundation of memory interfacing.
Address Decoding Techniques
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Now, letβs discuss address decoding logic. Can anyone explain why it's essential?
Is it to make sure that only one memory chip responds to a particular address?
Exactly! To achieve this, we must decode the higher order address lines to generate unique chip select signals.
What kind of logic do we use for decoding?
Typically, we employ logic gates or dedicated decoder ICs like the 74LS138. The output helps in activating only one chip at a time, ensuring efficient data access.
Can we visualize this with a simple circuit example?
Of course! Imagine we have a 5-input NOR gate connected to several address lines; this setup will help us create the necessary signals to chip select. Now, can anyone summarize what we discussed today?
We learned how to prevent memory address conflicts by using chip select signals generated through address decoding!
Implementation of Memory Operations
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Letβs dive into the specifics of memory operations. Can anyone describe what happens during a memory read operation?
The microprocessor places the address on the bus and activates the read control signal, right?
Absolutely correct! And the selected memory chip outputs the data onto the data bus. What about the write operation?
For writing, the microprocessor places the address and data on the bus, then activates the write control signal.
That's right! And how does this process vary for RAM versus ROM?
With RAM, we write data both ways, but ROM only allows reading.
Perfect! Understanding these operations is critical for interfacing different types of memory with our microprocessor.
Using the 8085 Trainer Kit
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Now that we understand the theory, let's discuss how we will implement this on the 8085 trainer kit. Whatβs our first step?
We need to design our memory map based on our RAM and ROM configuration!
Excellent! Once the map is ready, what comes next?
We set up the physical connections between the 8085 and the memory chips.
Correct! Make sure we follow the address decoding schematic as described. Finally, how can we verify our implementation?
By executing our assembly programs and monitoring the results in the memory locations.
Great recap! We will now proceed to get hands-on with the trainer kit, applying everything weβve discussed in the theoretical sessions.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
In this section, students learn to design a memory map for given RAM and ROM configurations, identify critical components like address buses and decoding logic, and understand the read/write processes involved in interfacing memory with the 8085 microprocessor. The importance of memory mapping and control signals is emphasized to ensure proper memory operation.
Detailed
Detailed Summary
In this section, we explore the crucial principles of memory interfacing with the 8085 microprocessor, focusing on how to effectively design a memory map and the schematics for interfacing memory devices. Memory is essential for storing data and programs in microprocessor systems, and understanding its architecture is key to successful interfacing.
Key Concepts Explored:
- Memory Map Design: The memory map provides a visual allocation of the 8085 microprocessor's address space (64 KB) to various memory chips (both RAM and ROM). This ensures clarity about where each component sits within the addressable range.
- Address Buses and Control Signals: We delve into how the 8085 uses an address bus of 16-bit (A0-A15) and an 8-bit data bus (D0-D7), and how control signals like overlineRD, overlineWR, and IO/overlineM facilitate the proper read/write operations.
- Types of Memory: The chapter distinguishes between Read-Only Memory (ROM), which is non-volatile and store firmware, and Random Access Memory (RAM), which is volatile and temporarily holds active data. Understanding the different memory types assists in their appropriate interface design.
- Address Decoding: We elaborate on address decoding techniques, including the use of logic gates or decoder ICs to generate unique Chip Select signals for each memory chip while avoiding overlap in address allocation.
- Memory Operation Cycles: The section describes the sequences involved in memory read and write operations, including the necessary configurations and control signals involved.
From this foundation, students will gain practical experience through assembly language programming, culminating in an understanding of how to utilize the 8085 microprocessor trainer kit to execute these concepts.
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Memory Configuration
Chapter 1 of 7
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Chapter Content
- Given Memory Configuration:
- ROM: 2 KB
- RAM: 4 KB
Detailed Explanation
In this first step, we define the memory configuration for our microprocessor system. We have two types of memory chips: a Read-Only Memory (ROM) chip that can store 2 Kilobytes (KB) of data and a Random Access Memory (RAM) chip that can store 4 KB of data. It's crucial to specify these sizes as they determine how many memory locations we can utilize for storing data and programs.
Examples & Analogies
Think of ROM as a bookshelf where you permanently store your favorite books (data that doesn't change), while RAM is like a whiteboard where you jot down your ideas and to-do lists (data that is temporary and frequently changed).
Address Lines Calculation
Chapter 2 of 7
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Chapter Content
- Calculate Address Lines Required for Each Chip:
- ROM (2KB): 2*1024=2048 bytes. Requires log_2(2048)=11 address lines (A0-A10).
- RAM (4KB): 4*1024=4096 bytes. Requires log_2(4096)=12 address lines (A0-A11).
Detailed Explanation
To communicate effectively with the memory chips, we need to determine how many address lines are required. For the ROM, since it can hold 2048 bytes (2 KB), we use logarithmic calculations to find that 11 address lines are needed (from A0 to A10). Similarly, for the RAM, which holds 4096 bytes (4 KB), we calculate that 12 address lines (A0 to A11) will be necessary. This indicates how the 8085 microprocessor can access each byte of memory.
Examples & Analogies
Imagine that each address line is like a piece of a postal address needed to locate a specific house in a neighborhood. If you need to deliver mail to a house with a larger number of addresses (like more RAM), you might need more parts in your address formulation, thus requiring more 'address lines' to ensure delivery.
Memory Address Assignment
Chapter 3 of 7
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Chapter Content
- Assign Memory Addresses and Create Memory Map:
- ROM: Assign starting address 0000H.
- Ending Address = 0000H+2048β1=07FFH.
- Address Range: 0000Hβ07FFH.
- RAM: Assign starting address 2000H (leaving a gap for other potential devices/expansion).
- Ending Address = 2000H+4096β1=2FFFH.
- Address Range: 2000Hβ2FFFH.
Detailed Explanation
After determining the necessary address lines, we assign specific memory addresses. The ROM starts at address 0000H and occupies addresses up to 07FFH, which corresponds to its 2 KB size. Meanwhile, the RAM starts at address 2000H, allowing space for possible future memory devices or expansions, and extends up to address 2FFFH. This planning helps in creating a memory map that clearly demarcates where each type of memory resides.
Examples & Analogies
Think of this step as laying a foundation for a new neighborhood. The ROM is like homes built on a series of consecutive lots (addresses 0000H to 07FFH), while the RAM is like new homes built further down the street (starting at 2000H) to allow space for parks or new buildings later.
Complete Memory Map Table
Chapter 4 of 7
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Chapter Content
- Complete Memory Map Table:
| Memory Device | Size | Starting Address | Ending 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
We now compile all of our calculations and assignments into a structured table, which serves as our memory map. This table contains essential details, such as the type of memory device (ROM or RAM), its size, starting and ending addresses, and the specific address lines used for chip selection. This organized layout provides a clear overview of how our memory is allocated and accessed.
Examples & Analogies
A memory map table is akin to an inventory list used in a library. Each entry notes the location (address) of every book (data) and ensures that all books (memory) can be accessed without confusion or overlap.
Address Decoding Logic Design
Chapter 5 of 7
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Chapter Content
- Design Address Decoding Logic and Interfacing Schematic:
- Common Connections:
- 8085 A0-A10 to ROM A0-A10.
- 8085 A0-A11 to RAM A0-A11.
- 8085 D0-D7 to ROM D0-D7 and RAM D0-D7.
- 8085 overlineRD to ROM overlineOE and RAM overlineOE.
- 8085 overlineWR to RAM overlineWE (ROM does not have overlineWE).
Detailed Explanation
In this step, we establish the necessary connections between the 8085 microprocessor and the RAM/ROM chips. The address lines from the microprocessor are connected to the respective address lines of the ROM and RAM. Similarly, we connect the data bus lines and control signals (read/write). This setup ensures that the microprocessor can communicate properly with the memory devices during data transfer operations.
Examples & Analogies
Creating address decoding logic is similar to wiring a sound system in a house. Each speaker (ROM or RAM) must be connected to the sound system (microprocessor) in a specific way so that signals (data) can flow smoothly to the right places without interference.
Chip Select Signal Generation
Chapter 6 of 7
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Chapter Content
β Chip Select (overlineCS) Generation:
- For ROM (0000Hβ07FFH): Requires A15=0, A14=0, A13=0, A12=0, A11=0.
- Decoding logic: Connect A11, A12, A13, A14, A15 to a 5-input NOR gate.
The output of the NOR gate connects to the ROM's overlineCS.
- For RAM (2000Hβ2FFFH): Requires A15=0, A14=0, A13=0, A12=1.
- Decoding logic: Connect A15, A14, A13 (inverted) and A12 (direct) to a 4-input AND gate. The output of the AND gate connects to the RAM's overlineCS.
Detailed Explanation
To ensure accurate access to each memory chip without conflicts, we generate a Chip Select signal. The conditions for the signal depend on the address lines. For the ROM, specific high and low states of the address lines (A15 to A11 being low) activate the chip selection, while for the RAM, A12 needs to be high. Logical gates (like NOR and AND) used in this design facilitate this process. This logic ensures that only one memory device responds at any memory access.
Examples & Analogies
Imagine a traffic system where traffic lights control which car gets to go at an intersection. The Chip Select signal acts like those lights, ensuring that only one car (memory device) is allowed to 'go' (respond) at a time, preventing accidents (data conflicts).
Master Memory Enable and Schematic Finalization
Chapter 7 of 7
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Chapter Content
β Master Memory Enable: The IO/overlineM signal (low for memory operations) should be incorporated into the overall chip select logic for each device (e.g., ANDed with the address decode output before connecting to overlineCS).
β Conceptual Interfacing Diagram (similar to Theory section, to be drawn clearly in the practical file): ...
Detailed Explanation
The final step involves the incorporation of the IO/overlineM signal, which indicates whether the operation is targeting memory or I/O devices. This signal must be part of the chip select logic, ensuring that the memory chips receive the correct signals only when needed. A clear, conceptual diagram representing these connections can be drawn in the practical file to facilitate understanding and reference.
Examples & Analogies
This is like ensuring that the lights in a smart home system are only activated when there is a need (IO/overlineM signal). This prevents unnecessary energy consumption in devices (preventing memory access when not needed), making the system more efficient and organized.
Key Concepts
-
Memory Map Design: The memory map provides a visual allocation of the 8085 microprocessor's address space (64 KB) to various memory chips (both RAM and ROM). This ensures clarity about where each component sits within the addressable range.
-
Address Buses and Control Signals: We delve into how the 8085 uses an address bus of 16-bit (A0-A15) and an 8-bit data bus (D0-D7), and how control signals like overlineRD, overlineWR, and IO/overlineM facilitate the proper read/write operations.
-
Types of Memory: The chapter distinguishes between Read-Only Memory (ROM), which is non-volatile and store firmware, and Random Access Memory (RAM), which is volatile and temporarily holds active data. Understanding the different memory types assists in their appropriate interface design.
-
Address Decoding: We elaborate on address decoding techniques, including the use of logic gates or decoder ICs to generate unique Chip Select signals for each memory chip while avoiding overlap in address allocation.
-
Memory Operation Cycles: The section describes the sequences involved in memory read and write operations, including the necessary configurations and control signals involved.
-
From this foundation, students will gain practical experience through assembly language programming, culminating in an understanding of how to utilize the 8085 microprocessor trainer kit to execute these concepts.
Examples & Applications
If we have a 4KB RAM, it occupies an address range from 2000H to 2FFFH.
Address decoding can be achieved with an AND gate for CS generation from multiple address lines.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
A memory map shows each chip's space,
Stories
Imagine a library where each book represents a memory chip. The address bus is the librarian who guides you to the right aisle without mixing the books. The address decoding is like the categories assigned which ensure only one section is opened at a time to find your desired book.
Memory Tools
FOR MEMORY: Formulate Organization Ram Mapping Effortlessly Maintain Overlapping Restrictions Yearly.
Acronyms
CHIP
**C**ontrol signals
**H**igh Address lines
**I**nterfacing **P**erformance.
Flash Cards
Glossary
- Memory Map
A representation of how the microprocessor's address space is allocated among various memory devices.
- Address Bus
A collection of wires that carries the address signals to access memory locations.
- Control Signals
Signals that manage how data moves between the microprocessor and memory.
- ReadOnly Memory (ROM)
Non-volatile memory used for permanent storage where data is only read.
- Random Access Memory (RAM)
Volatile memory used for temporary storage where data can be both read and written.
- Address Decoding
The process of determining which memory chip to access based on the address provided.
- Chip Select (CS)
A signal that enables a specific memory chip, allowing it to respond to the microprocessor's requests.
Reference links
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