Program to Read Data from Memory (RAM/ROM)
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Introduction to Memory Interfacing
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Today, we're going to explore how memory is interfaced with the 8085 microprocessor. Do you all know why memory is crucial for systems?
It's important because a microprocessor needs memory to store data and programs.
Exactly! The 8085 can address 64KB of memory. This is done using a 16-bit address bus. Can anyone tell me how many memory locations can it actually address?
It can address 65,536 locations because 2 raised to the power of 16 is 65,536.
That's right! Now, let's remember this formula: 2^n = Number of locations, where n is the address bit. Now can anyone differentiate between RAM and ROM?
RAM is volatile memory used for temporary storage, while ROM is non-volatile, used for permanent storage.
Good job! Remember, RAM allows both read and write operations, while ROM only allows read. Let's dive deeper into memory mapping.
Memory Mapping and Address Decoding
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Let's talk about memory maps. A memory map represents how the 64KB address space is allocated. What do you think happens without proper mapping?
Without mapping, two devices might try to use the same address, causing conflicts.
Exactly! Address decoding is critical to prevent this. We use higher-order address lines to generate chip select signals. What components can we use for address decoding?
We can use logic gates like AND and OR or dedicated decoder ICs like the 74LS138.
Correct! Now, let's apply this knowledge to design a memory map for a ROM and RAM configuration.
Designing a Memory Map
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We have a RAM and a ROM configuration to map. Who can help me calculate the address lines required for a 2KB ROM and a 4KB RAM?
The ROM needs 11 address lines, and the RAM needs 12 because 2^11 is 2048 and 2^12 is 4096.
Perfect! Now, let's assign the addresses. What would be the starting and ending addresses for the ROM?
The ROM starts at 0000H and ends at 07FFH.
Great! And for the RAM?
The RAM starts at 2000H and ends at 2FFFH.
Exactly! This is how we define a clear memory map. Now let's move on to programming.
Assembly Language Programming
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Now that we have our memory map, let's look at some assembly language programs. Who can share the purpose of writing data to a RAM location?
To store data in memory for later retrieval.
Exactly! The program uses the `MOV` instruction to write to a specific memory address. What are some key instructions we will use?
`LXI`, `MVI`, and `MOV` are some of the instructions used.
Great! Now let's look at the reading operation. Why is it essential to move data from memory to a register?
So we can manipulate or use the data in the CPU's registers for processing.
Exactly! You are grasping the concept well. Now let's prepare to verify these operations on the trainer kit.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section outlines the fundamental principles of memory interfacing with the 8085 microprocessor, detailing memory mapping, address decoding, and the execution of assembly language programs to read from and write to memory locations, using RAM and ROM as examples.
Detailed
Detailed Summary of Memory Interfacing with 8085
This section provides an exploration of the principles underlying memory interfacing with the 8085 microprocessor. It begins by explaining the importance of memory in storing programs and data within any microprocessor system. The 8085 features a 16-bit address bus, enabling it to address up to 64KB of memory. Memory types are classified into ROM, which is non-volatile and used for permanent data storage, and RAM, which is volatile and utilized for temporary data storage. The section delves into the concept of a memory map, a visual representation of how address ranges are allocated among memory devices and peripherals. Following this, it elucidates the mechanisms of address decoding, crucial for ensuring that the correct chip responds to any given address.
To practically demonstrate these concepts, the section outlines a procedure to design a memory map for a specific ROM and RAM configuration, explains the assembly language programming to read from and write to memory, and describes how to verify these operations using an 8085 trainer kit. By the end of the section, students should possess a solid understanding of memory interfacing, culminating in practical experience through programming and debugging.
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Overview of Memory Read Operation
Chapter 1 of 3
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Chapter Content
Memory Read:
The 8085 places the 16-bit address on the address bus, sets IO/overlineM low, and activates overlineRD (low). The selected memory chip places its data onto the data bus, which the 8085 then reads.
Detailed Explanation
In a memory read operation, the 8085 microprocessor needs to access data stored in memory, whether it's in RAM or ROM. First, it specifies the location of the desired data by placing a 16-bit address onto the address bus. After this, it signals that it wants to read data by setting the IO/overlineM signal to low, which indicates that a memory operation is taking place. Finally, it activates the overlineRD signal, which tells the selected memory chip to put its data onto the data bus so the processor can read it.
Examples & Analogies
Think of the microprocessor as a librarian wanting to fetch a book (data) from a shelf (memory). The address bus is like giving the librarian the specific shelf number (address) where the book is located. The IO/overlineM signal is like the librarian asking for the book to be retrieved. When the librarian activates the read signal, it's like saying, 'Please hand me the book,' so that the book can be taken off the shelf and handed over.
Overview of Memory Write Operation
Chapter 2 of 3
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Chapter Content
Memory Write:
The 8085 places the 16-bit address on the address bus, sets IO/overlineM low, places the 8-bit data on the data bus, and activates overlineWR (low). The selected memory chip then latches the data from the data bus into the addressed location.
Detailed Explanation
For a memory write operation, the 8085 must specify where to store the data and what data to write. It begins by placing a 16-bit address on the address bus to indicate where the data should go. The IO/overlineM signal is again set to low to signify that a memory operation is occurring. Following this, the 8-bit data that needs to be written is placed onto the data bus. Finally, the processor activates the overlineWR signal to instruct the memory chip to store the data at the specified address.
Examples & Analogies
Imagine the microprocessor as a store manager who wants to add new inventory (data) to a specific shelf (address). The address bus is the shelf number given to the manager, indicating where the inventory should be placed. When the manager sets the IO/overlineM signal low, it's like getting ready to add new items. By placing new items on the data bus, the manager gathers everything that needs to be stored. Activating the overlineWR signal is akin to the manager saying, 'Put these items on the shelf now,' so that the items are correctly placed in the right location.
Assembly Language Program to Read Data
Chapter 3 of 3
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Chapter Content
Program to Read Data from Memory (RAM/ROM)
- 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
Detailed Explanation
This assembly language program is a straightforward way to read data from memory. It starts with the ORG directive, which sets the starting address of the program in ROM. The LXI instruction loads the 16-bit memory address 2050H into the HL register pair. The MOV A, M instruction then moves the data currently stored at that memory location (pointed to by HL) into the Accumulator (register A). Finally, the content of the Accumulator is transferred to register B with the MOV B, A instruction. The program ends with HLT, which halts the processor.
Examples & Analogies
Consider this program as a series of steps taken by a student who wants to retrieve a note from a friend's locker. The student first goes to the locker (memory address 2050H) by remembering the specific locker number (loading the address into HL). Next, the student opens the locker and takes the note out (reading the data into register A) and then passes the note to another friend (moving the data into register B). Finally, the student stops their actions by concluding their task (hitting the halt instruction).
Key Concepts
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Address Bus: The set of lines that carry addresses from the microprocessor to the memory components.
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Chip Select: Signals that determine which memory chip will communicate with the microprocessor.
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Read/Write Operations: Processes by which data is read from or written to RAM/ROM.
Examples & Applications
Example of memory map: A ROM of 2KB (0000Hβ07FFH) and RAM of 4KB (2000Hβ2FFFH).
In an assembly program, the instruction LXI H, 2050H loads the address 2050H into the HL register pair.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
ROM is read, RAM is right, once you write, it takes flight.
Stories
Imagine a library (RAM) where books can be borrowed (written) and returned (read), versus a museum (ROM) where displays can only be viewed.
Memory Tools
R-A-M for 'Read and Manage' and R-O-M for 'Read-Only Memory'.
Acronyms
M.A.P - Memory Allocation Process, which helps remember memory mapping.
Flash Cards
Glossary
- RAM
Random Access Memory, a volatile memory used for temporary storage.
- ROM
Read-Only Memory, a non-volatile memory used for permanent data storage.
- Memory Map
A visual representation of how memory addresses are allocated for devices.
- Address Bus
A set of wires used to carry memory addresses from the microprocessor to memory.
- Address Decoding
The process of determining which memory chip should respond to a memory address.
Reference links
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