8085 Microprocessor: Architecture & Support Components

Contents Pin diagram of Operations Architecture of Communication with Memory

Pinout Diagram of 8085 A 40-pin IC Six groups of signals Address Bus Data Bus Control and Status pins Power Supply & frequency signals Externally initiated Signals Serial I/O ports

Logic Pinout of 8085 Data Bus Address Bus Control & Status Externally initiated signals Serial I/O ports Power Supply & frequency

8085 Operations Microprocessor Initiated Operations Internal Operations Peripheral/Externally Initiated Operations

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

Architecture of 8085 Power Supply – a +5V DC power supply Maximum clock frequency of 3MHz 8-bit general purpose microprocessor 16-bit Address Bus Capable of addressing 64K of memory

Architecture of 8085

Architecture 0f 8085 Cont… ALU Timing and Control Unit General Purpose Registers Program Status word Program Counter Stack Pointer Instruction Register and Decoder Interrupt Control Serial I/O Control Address Bus Data Bus

Architecture 0f 8085 Cont… Arithmetic Logic Unit (ALU) 8085 has 8-bit ALU Performs arithmetic & Logic operations on data Timing & Control Unit Generates timing and control signals General Purpose Registers 8-bit registers (B,C,D,E,H,L) 16-bit register pairs (BC, DE, HL,PSW)

Architecture 0f 8085 Cont… Program Status Word (PSW) Accumulator and Flag Register can be combined as a register pair called PSW Instruction Register and Decoder Instruction fetched from memory is stored in Instruction register (8-bit register) Decoder decodes the instruction and directs the Timing & Control Unit accordingly

Architecture 0f 8085 Cont… Interrupt Control 8085 has 5 interrupt signals INTR – general purpose interrupt RST 5.5Restart Interrupts RST 6.5 RST 7.5 TRAP – non-maskable interrupt The interrupts listed above are in increasing order of priority

Architecture 0f 8085 Cont… Serial I/O Control 8085 has two signals for serial communication SID – Serial Input Data SOD – Serial Output Data

Architecture 0f 8085 Cont… Address Bus Used to address memory & I/O devices 8085 has a 16-bit address bus A 15 A 14 A 13 A 12 A 11 A 10 A9A9 A8A8 AD 7 AD 6 AD 5 AD 4 AD 3 AD 2 AD 1 AD 0 Lower-order Address Higher-order Address Data Bus Used to transfer instructions and data 8085 has a 8-bit data bus Data Bus

8085 Communication with Memory Involves the following three steps 1. Identify the memory location (with address) 2. Generate Timing & Control signals 3. Data transfer takes place

Example: Memory Read Operation 1 2 3

1 2 3

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… 8085Memory A8-A15 20H AD0-AD7 05H RD 4FH 2005H

8085 Interfacing with Memory chips 8085 Memory Interface Memory Chip Address Data Control Address Data Control

8085 Interfacing with Memory chips 8085 Memory Interface Memory Chip AD0-AD7 Control A0 – A7 Data 74LS373 A8-A15 ALE

8085 Interfacing with Memory chips 8085 Memory Interface Program Memory AD0-AD7 IO/M A0 – A7 Data 74LS373 A8-A15 ALE RD CS

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 0000 A 11 to A 0 A 15 A 14 A 13 A 12 0…. 0 0 = 0000H 1111 A 11 to A 0 A 15 A 14 A 13 A 12 1…. 111 = FFFFH to

Interfacing I/O devices with 8085 Peripheral-mapped I/O & Memory-mapped I/O

Interfacing I/O devices with I/O Interface I/O Devices Memory Interface Memory Devices System Bus

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 1. Identify the I/O device (with address) 2. Generate Timing & Control signals 3. 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) 1. Memory-mapped I/O (16-bit address) 2. 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 3. Data transfer takes place

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

Show the Pinout of 8085 in several grpups. Mention the operations of 8085 in group Discuss the data bus and address bus and the multiplexing. Short questions