Skip to main content

Branching Group Instructions (Part-IV) - PCHL and RST n

By
PCHL:
  • This instruction loads the contents of HL register pair into the program counter (PC).
  • Thus the program control is transferred to the address given in HL register pair.
  • No flags are affected.
  • It is a one byte instruction.
  • Register addressing mode is used.
Example:
If HL = 4000H
PCHL ; This instruction will load PC with 4000H and program control is transferred at 4000H.

RST n:
  • This instruction transfers the program control to the specific memory location.
  • It is like a CALL instruction but in this instruction, the program control is transferred to a fixed address.
  • These fixed addresses are called vector addresses.
  • The processor calculates these vector addresses by multiplying RST number i.e. n by 8.
  • Just like CALL instruction, before transferring the program control to the vector address, it saves the current contents of program counter on the stack.
  • No flags are affected.
  • It is a one byte instruction.
  • Register indirect addressing mode is used.
Example:
If SP = 4000H
2000H RST 6 ; This instruction will copy the current contents of PC i.e. 2001H on the stack and it will load the PC with vector address 0030H (6 * 8 = 48 in decimal = 0030H).
Labels:

Comments

Post a Comment

Popular posts from this blog

Program to pack the two unpacked BCD numbers

By
Statement: Pack the two unpacked BCD numbers stored in memory locations 2000H and 2001H and store the result in memory location 2002H. The least significant digit is stored at 2000H. Example: (2000H) = 04H (2001H) = 09H Result = (2002H) = 94H Program: LDA 2001H                        ; Obtain the most significant BCD digit RLC                                    ; Rotate left  RLC                                    ; Rotate left  RLC                                    ; Rotate left  RLC                                    ; Rotate left...
Post a Comment
Read more

Program to exchange the contents of two memory locations

By
Statement: Exchange the contents of memory locations 2000H and 2001H. Example:  Initially, (2000H) = 34H (2001H) = 20H After exchanging, (2000H) = 20H (2001H) = 34H Program 1 using direct addressing instructions: LDA 2000H               ; Get the contents of location 2000H into accumulator MOV B, A                  ; Move the contents of accumulator into register B LDA 2001H                ; Get the contents of location 2001H into accumulator STA 2000H                 ; Store the contents of accumulator into location 2000H MOV A, B                  ; Move the contents of register B into accumulator STA 2001H                 ; Store the contents of accumulator into location 2001H HLT  ...
Post a Comment
Read more

Program to add the contents of two memory locations

By
Statement: Add the contents of memory locations 2000H and 2001H and place the result in the memory locations 2002H and 2003H. Example: (2000H) = C3H (2001H) = 29H Result = C3H + A9H = 016CH (2002H) = 6CH (2003H) = 01H Program: LXI H, 2000H                   ; HL points to location 2000H MOV A, M                        ; Move the contents of 2000H into accumulator INX H                                ; HL points to location 2001H ADD M                              ; Add the contents of 2001H with the contents of accumulator INX H                                ; HL points to location 2002H MOV M, A      ...
Post a Comment
Read more