How many T sates are required to execute STA 1234 instruction:

SOLUTION

• The time taken to execute an instruction is called the instruction cycle.
• Time taken to execute are operation is known as the machine cycle.
• Generally, one instruction will contain 1 to 5 machine cycles.
• The portion of the machine cycle executed in one internal clock pulse is known as T-state.
• T-state starts at the falling edge of a clock pulse.

Various operations performed by 8085 are:

• Opcode fetch and execute: Most of the instruction needs 4T-states, but some instruction needs more than 4T-states. For Ex- HLT, CALL, DCX, etc
• Memory Read – 3T
• Memory write – 3T
• I/O read – 3T
• I/O write – 3T

“STA 1234” means store from ‘A’ register to the memory location.

It is a 3-byte instruction.

The opcode fetch and execute – 4T

1^st-byte address fetch – 3T

2^nd-byte address fetch – 3T

Write to memory (from A) – 3T

Total - 13 T states