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

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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).
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