Download to read offline
Uploaded bysandip das
1. 8085 fetch cycle
The document describes the opcode fetch cycle of the 8085 microprocessor. It contains a block diagram of the main components involved in the opcode fetch cycle, including the program counter, address latch, memory, and instruction register. It also includes a timing diagram that shows the clock signals and control signal timings during an opcode fetch cycle, such as the addressing of memory to retrieve the opcode. The opcode is then stored in the instruction register to be decoded by the microprocessor.
More Related Content
More from sandip das
1. 8085 fetch cycle
- 1. MICROPROCESSOR 8085 OPCODE FETCHCYCLE LECTURE 4 PROF. SANDIP DAS
- 2. B C D E HL Stack Pointer(SP) Program Counter(PC) Incrementer/Dec rementer Address Latch ADDRESS BUFFER DATA/ADDRESS BUFFER 8 BIT INTERNAL DATA BUS INSTRUCTIO N REGISTER INSTRUCTIO N DECODER TIMING AND CONROL UNIT STATUS FLAGS ALU TEMPORAR Y REGISTER ACCUMUL A-TOR INTERRUPT CONTROL SERIAL I/O CONTROL CLK 𝑅𝐷 𝑊𝑅 ALE 𝑆0 𝑆1 CONTROL SIGNALS INTERRUPT SIGNALS 𝑋1 𝑋2 𝐴8 − 𝐴15 𝐴𝐷0 − 𝐴𝐷7
- 3. OPCODE FETCH OPERATION B C DE H L Stack Pointer(SP) PC Incrementer/Decr ementer Address Latch ADDRESS BUFFER DATA/ADDRES S BUFFER 8 BIT INTERNAL DATA BUS INSTRUCTION REGISTER INSTRUCTION DECODER TIMING AND CONROL UNIT ALU ACCUMUL A-TOR CLK 𝑅𝐷 𝑊𝑅 ALE 𝑆0 𝑆1 CONTROL SIGNALS 𝑋1 𝑋2 MAR MDR AC 1A DB MEMORY (8000) (8000) (8000) (DB) (DB)
- 4. STATUS SIGNALS 𝑺 𝟏𝑺 𝟎 Operation 0 0 HALT 0 1 WRITE 1 0 READ 1 1 FETCH When 𝐼𝑂/ 𝑀=0, Microprocessor performs memory related operation When 𝐼𝑂/ 𝑀=1, Microprocessor performs IO related operation
- 5. OPCODE FETCH CYCLE(TIMING DIAGRAM) CLOCK 𝑇1 𝑇2 𝑇3 𝑇4 𝐴15- 𝐴8 𝐴𝐷0 − 𝐴𝐷7 ALE 𝐼𝑂/ 𝑀 𝑆1, 𝑆0 𝑅𝐷 HIGHER ORDER M ADDRESS LOWER ORDER M ADDRESS OPCODE 𝐷0 − 𝐷7 UNSPECIFIE D