Timing Diagram Of Lhld Instruction In 8085 Instant

The (Load H and L registers direct) instruction in the 8085 microprocessor is a 3-byte instruction that loads the contents of a specific 16-bit memory address into the H-L register pair . It is one of the most complex instructions in terms of timing, requiring 5 machine cycles and 16 T-states to complete. 1. Instruction Overview Opcode : 2Bh (for LHLD)

: The processor places the 16-bit address it just "learned" onto the address bus. It reads the byte at that location and stores it in the L register .

: The PC places the address on the bus; ALE latches it. The processor fetches 2Bh . In T4cap T sub 4 Timing Diagram Of Lhld Instruction In 8085

) : Carries the most significant bits of the memory address throughout the cycle. : Acts as the lower address bus during T1cap T sub 1 Acts as the data bus during T2cap T sub 2 T3cap T sub 3 to fetch the opcode or read memory data. Control Signals ( RD¯modified cap R cap D with bar above WR¯modified cap W cap R with bar above ) : Since LHLD is a "Load" instruction, WR¯modified cap W cap R with bar above remains high (inactive). RD¯modified cap R cap D with bar above goes low during T2cap T sub 2 T3cap T sub 3 of all five cycles to enable memory reading. Status Signals ( ) : (Memory operation). For Opcode Fetch (M1): For Memory Read (M2-M5): 4. Step-by-Step Execution

: 5 (Opcode Fetch, Memory Read, Memory Read, Memory Read, Memory Read) T-States : 2. Breakdown of Machine Cycles The timing diagram is divided into five distinct phases: Machine Cycle Description M1 Opcode Fetch 4 T-states Fetches the opcode 2Bh from memory. M2 Memory Read 3 T-states Reads the lower-byte of the 16-bit address ( M3 Memory Read 3 T-states Reads the higher-byte of the 16-bit address ( M4 Memory Read 3 T-states The (Load H and L registers direct) instruction

: The processor increments the address by 1, reads the next byte, and stores it in the H register .

(L)←[[adr]]open paren cap L close paren left arrow open bracket open bracket a d r close bracket close bracket (Content of memory address moves to L) Instruction Overview Opcode : 2Bh (for LHLD) :

(H)←[[adr+1]]open paren cap H close paren left arrow open bracket open bracket a d r plus 1 close bracket close bracket (Content of memory address moves to H)