09-06-2012, 02:01 PM
8085 Microprocessor
8085 Microprocessor.ppt (Size: 1.35 MB / Downloads: 129)
Microprocessor Initiated Operations
Memory Read
Memory Write
I/O Read
I/O Write
Internal Operations
Store 8-bit data
Perform Arithmetic and Logic Operations
Test for conditions
Sequence the execution of instructions
Store/Retrieve data from stack during execution
Peripheral/Externally Initiated Operations
Reset
Interrupt
Ready
Hold
8085 Communication with Memory
Involves the following three steps
Identify the memory location (with address)
Generate Timing & Control signals
Data transfer takes place
Example: Memory Read Operation
Timing Diagram
Demultiplexing Address/Data Bus
8085 identifies a memory location with its 16 address lines, (AD0 to AD7) & (A8 to A15)
8085 performs data transfer using its data lines, AD0 to AD7
Lower order address bus & Data bus are multiplexed on same lines i.e. AD0 to AD7.
Demultiplexing refers to separating Address & Data signals for read/write operations
Need for Demultiplexing…
The 16-bit address of the memory location must be applied to the memory chip for the whole duration of the memory read/write operation.
Lower-order address needs to be saved before microprocessor uses it for data transfer
8085 Interfacing with Memory chips
8085 Interfacing with Memory chips
8085 Interfacing with Memory chips
Memory Mapping
8085 has 16-bit Address Bus
The complete address space is thus given by the range of addresses 0000H – FFFFH
The range of addresses allocated to a memory device is known as its memory map
Memory map: 64K memory device
Address lines required: 16 (A0 – A15)
Memory map: 0000H - FFFFH
So the memory map is
Interfacing I/O devices with 8085
Peripheral-mapped I/O
&
Memory-mapped I/O
Interfacing I/O devices with 8085
Techniques for I/O Interfacing
Memory-mapped I/O
Peripheral-mapped I/O
Memory-mapped I/O
8085 uses its 16-bit address bus to identify a memory location
Memory address space: 0000H to FFFFH
8085 needs to identify I/O devices also
I/O devices can be interfaced using addresses from memory space
8085 treats such an I/O device as a memory location
This is called Memory-mapped I/O
Peripheral-mapped I/O
8085 has a separate 8-bit addressing scheme for I/O devices
I/O address space: 00H to FFH
This is called Peripheral-mapped I/O or I/O-mapped I/O
8085 Communication with I/O devices
Involves the following three steps
Identify the I/O device (with address)
Generate Timing & Control signals
Data transfer takes place
8085 communicates with a I/O device only if there is a Program Instruction to do so
1.Identify the I/O device (with address)
Memory-mapped I/O (16-bit address)
Peripheral-mapped I/O (8-bit address)
2.Generate Timing & Control Signals
Memory-mapped I/O
Reading Input: IO/M = 0, RD = 0
Write to Output: IO/M = 0, WR = 0
Peripheral-mapped I/O
Reading Input: IO/M = 1, RD = 0
Write to Output: IO/M = 1, WR = 0
8085 Communication with I/O devices
Involves the following three steps
Identify the I/O device (with address)
Generate Timing & Control signals
Data transfer takes place
8085 communicates with a I/O device only if there is a Program Instruction to do so
Peripheral I/O Instructions
IN Instruction
Inputs data from input device into the accumulator
It is a 2-byte instruction
Format: IN 8-bit port address
Example: IN 01H
OUT Instruction
Outputs the contents of accumulator to an output device
It is a 2-byte instruction
Format: OUT 8-bit port address
Example: OUT 02H
Example Program
WAP to read a number from input port (port address 01H) and display it on ASCII display connected to output port (port address 02H)
IN 01H ;reads data value 03H (example)into ;accumulator, A = 03H
MVI B, 30H;loads register B with 30H
ADD B ;A = 33H, ASCII code for 3
OUT 02H ;display 3 on ASCII display
Memory-mapped I/O Instructions
I/O devices are identified by 16-bit addresses
8085 communicates with an I/O device as if it were one of the memory locations
Memory related instructions are used
For e.g. LDA, STA
LDA 8000H
Loads A with data read from input device with 16-bit address 8000H
STA 8001H
Stores (Outputs) contents of A to output device with 16-bit address 8001H
Example Program
WAP to read a number from input port (port address 8000H) and display it on ASCII display connected to output port (port address 8001H)
LDA 8000H;reads data value 03H (example)into ;accumulator, A = 03H
MVI B, 30H;loads register B with 30H
ADD B ;A = 33H, ASCII code for 3
STA 8001H;display 3 on ASCII display
