01-08-2012, 10:17 AM
Microprocessor Architecture
[attachment=29783]
Microprocessor Architecture
The microprocessor can be programmed to perform functions on given data by writing specific instructions into its memory.
The microprocessor reads one instruction at a time, matches it with its instruction set, and performs the data manipulation specified.
The result is either stored back into memory or displayed on an output device.
The 8085 Architecture
The 8085 uses three separate busses to perform its operations
The address bus.
The data bus.
The control bus.
The Address Bus
16 bits wide (A0 A1…A15)
Therefore, the 8085 can access locations with numbers from 0 to 65,536. Or, the 8085 can access a total of 64K addresses.
“Unidirectional”.
Information flows out of the microprocessor and into the memory or peripherals.
When the 8085 wants to access a peripheral or a memory location, it places the 16-bit address on the address bus and then sends the appropriate control signals.
The Data Bus
8 bits wide (D0 D1…D7)
“Bi-directional”.
Information flows both ways between the microprocessor and memory or I/O.
The 8085 uses the data bus to transfer the binary information.
Since the data bus has 8-bits only, then the 8085 can manipulate data 8 bits at-a-time only.
The Control Bus
There is no real control bus. Instead, the control bus is made up of a number of single bit control signals.
Operation Types in a Microprocessor
All of the operations of the microprocessor can be classified into one of three types:
Microprocessor Initiated Operations
Internal Operations
Peripheral Initiated Operations
Microprocessor Initiated Operations
These are operations that the microprocessor itself starts.
These are usually one of 4 operations:
Memory Read
Memory Write
I/O Read (Get data from an input device)
I/O write (Send data to an output device)
Microprocessor Initiated Operations
It is important to note that the microprocessor treats memory and I/O devices the same way.
Input and output devices simply look like memory locations to the microprocessor.
For example, the keyboard may look like memory address A3F2H. To get what key is being pressed, the microprocessor simply reads the data at location A3F2H.
The communication process between the microprocessor and peripheral devices consist of the following three steps:
Identify the address.
Transfer the binary information.
Provide the right timing signals.
The Read Operation
To read the contents of a memory location, the following steps take place:
The microprocessor places the 16-bit address of the memory location on the address bus.
The microprocessor activates a control signal called “memory read” which enables the memory chip.
The memory decodes the address and identifies the right location.
The memory places the contents on the data bus.
The microprocessor reads the value of the data bus after a certain amount of time.
Internal Data Operations
The 8085 can perform a number of internal operations. Such as: storing data, Arithmetic & Logic operations, Testing for condition, etc.
To perform these operations, the microprocessor needs an internal architecture similar to the following:
The Internal Architecture
We have already discussed the general purpose registers, the Accumulator, and the flags.
The Program Counter (PC)
This is a register that is used to control the sequencing of the execution of instructions.
This register always holds the address of the next instruction.
Since it holds an address, it must be 16 bits wide.
The Internal Architecture
The Stack pointer
The stack pointer is also a 16-bit register that is used to point into memory.
The memory this register points to is a special area called the stack.
The stack is an area of memory used to hold data that will be retreived soon.
The stack is usually accessed in a Last In First Out (LIFO) fashion.
Externally Initiated Operations
External devices can initiate (start) one of the 4 following operations:
Reset
All operations are stopped and the program counter is reset to 0000.
Interrupt
The microprocessor’s operations are interrupted and the microprocessor executes what is called a “service routine”.
This routine “handles” the interrupt, (perform the necessary operations). Then the microprocessor returns to its previous operations and continues.
Externally Initiated Operations
Ready
The 8085 has a pin called RDY. This pin is used by external devices to stop the 8085 until they catch up.
As long as the RDY pin is low, the 8085 will be in a wait state.
Hold
The 8085 has a pin called HOLD. This pin is used by external devices to gain control of the busses.
When the HOLD signal is activated by an external device, the 8085 stops executing instructions and stops using the busses.
This would allow external devices to control the information on the busses. Example DMA.
The Design and Operation of Memory
Memory in a microprocessor system is where information (data and instructions) is kept. It can be classified into two main types:
Main memory (RAM and ROM)
Storage memory (Disks , CD ROMs, etc.)
The simple view of RAM is that it is made up of registers that are made up of flip-flops (or memory elements).
The number of flip-flops in a “memory register” determines the size of the memory word.
ROM on the other hand uses diodes instead of the flip-flops to permanently hold the information.
Accessing Information in Memory
For the microprocessor to access (Read or Write) information in memory (RAM or ROM), it needs to do the following:
Select the right memory chip (using part of the address bus).
Identify the memory location (using the rest of the address bus).
Access the data (using the data bus).
Tri-State Buffers
An important circuit element that is used extensively in memory.
This buffer is a logic circuit that has three states:
Logic 0, logic1, and high impedance.
When this circuit is in high impedance mode it looks as if it is disconnected from the output completely.
The Tri-State Buffer
This circuit has two inputs and one output.
The first input behaves like the normal input for the circuit.
The second input is an “enable”.
If it is set high, the output follows the proper circuit behavior.
If it is set low, the output looks like a wire connected to nothing.
The Basic Memory Element
The basic memory element is similar to a D latch.
This latch has an input where the data comes in. It has an enable input and an output on which data comes out.
[attachment=29783]
Microprocessor Architecture
The microprocessor can be programmed to perform functions on given data by writing specific instructions into its memory.
The microprocessor reads one instruction at a time, matches it with its instruction set, and performs the data manipulation specified.
The result is either stored back into memory or displayed on an output device.
The 8085 Architecture
The 8085 uses three separate busses to perform its operations
The address bus.
The data bus.
The control bus.
The Address Bus
16 bits wide (A0 A1…A15)
Therefore, the 8085 can access locations with numbers from 0 to 65,536. Or, the 8085 can access a total of 64K addresses.
“Unidirectional”.
Information flows out of the microprocessor and into the memory or peripherals.
When the 8085 wants to access a peripheral or a memory location, it places the 16-bit address on the address bus and then sends the appropriate control signals.
The Data Bus
8 bits wide (D0 D1…D7)
“Bi-directional”.
Information flows both ways between the microprocessor and memory or I/O.
The 8085 uses the data bus to transfer the binary information.
Since the data bus has 8-bits only, then the 8085 can manipulate data 8 bits at-a-time only.
The Control Bus
There is no real control bus. Instead, the control bus is made up of a number of single bit control signals.
Operation Types in a Microprocessor
All of the operations of the microprocessor can be classified into one of three types:
Microprocessor Initiated Operations
Internal Operations
Peripheral Initiated Operations
Microprocessor Initiated Operations
These are operations that the microprocessor itself starts.
These are usually one of 4 operations:
Memory Read
Memory Write
I/O Read (Get data from an input device)
I/O write (Send data to an output device)
Microprocessor Initiated Operations
It is important to note that the microprocessor treats memory and I/O devices the same way.
Input and output devices simply look like memory locations to the microprocessor.
For example, the keyboard may look like memory address A3F2H. To get what key is being pressed, the microprocessor simply reads the data at location A3F2H.
The communication process between the microprocessor and peripheral devices consist of the following three steps:
Identify the address.
Transfer the binary information.
Provide the right timing signals.
The Read Operation
To read the contents of a memory location, the following steps take place:
The microprocessor places the 16-bit address of the memory location on the address bus.
The microprocessor activates a control signal called “memory read” which enables the memory chip.
The memory decodes the address and identifies the right location.
The memory places the contents on the data bus.
The microprocessor reads the value of the data bus after a certain amount of time.
Internal Data Operations
The 8085 can perform a number of internal operations. Such as: storing data, Arithmetic & Logic operations, Testing for condition, etc.
To perform these operations, the microprocessor needs an internal architecture similar to the following:
The Internal Architecture
We have already discussed the general purpose registers, the Accumulator, and the flags.
The Program Counter (PC)
This is a register that is used to control the sequencing of the execution of instructions.
This register always holds the address of the next instruction.
Since it holds an address, it must be 16 bits wide.
The Internal Architecture
The Stack pointer
The stack pointer is also a 16-bit register that is used to point into memory.
The memory this register points to is a special area called the stack.
The stack is an area of memory used to hold data that will be retreived soon.
The stack is usually accessed in a Last In First Out (LIFO) fashion.
Externally Initiated Operations
External devices can initiate (start) one of the 4 following operations:
Reset
All operations are stopped and the program counter is reset to 0000.
Interrupt
The microprocessor’s operations are interrupted and the microprocessor executes what is called a “service routine”.
This routine “handles” the interrupt, (perform the necessary operations). Then the microprocessor returns to its previous operations and continues.
Externally Initiated Operations
Ready
The 8085 has a pin called RDY. This pin is used by external devices to stop the 8085 until they catch up.
As long as the RDY pin is low, the 8085 will be in a wait state.
Hold
The 8085 has a pin called HOLD. This pin is used by external devices to gain control of the busses.
When the HOLD signal is activated by an external device, the 8085 stops executing instructions and stops using the busses.
This would allow external devices to control the information on the busses. Example DMA.
The Design and Operation of Memory
Memory in a microprocessor system is where information (data and instructions) is kept. It can be classified into two main types:
Main memory (RAM and ROM)
Storage memory (Disks , CD ROMs, etc.)
The simple view of RAM is that it is made up of registers that are made up of flip-flops (or memory elements).
The number of flip-flops in a “memory register” determines the size of the memory word.
ROM on the other hand uses diodes instead of the flip-flops to permanently hold the information.
Accessing Information in Memory
For the microprocessor to access (Read or Write) information in memory (RAM or ROM), it needs to do the following:
Select the right memory chip (using part of the address bus).
Identify the memory location (using the rest of the address bus).
Access the data (using the data bus).
Tri-State Buffers
An important circuit element that is used extensively in memory.
This buffer is a logic circuit that has three states:
Logic 0, logic1, and high impedance.
When this circuit is in high impedance mode it looks as if it is disconnected from the output completely.
The Tri-State Buffer
This circuit has two inputs and one output.
The first input behaves like the normal input for the circuit.
The second input is an “enable”.
If it is set high, the output follows the proper circuit behavior.
If it is set low, the output looks like a wire connected to nothing.
The Basic Memory Element
The basic memory element is similar to a D latch.
This latch has an input where the data comes in. It has an enable input and an output on which data comes out.