Three byte instruction

The  instruction which  have 16  bit data address  as its  operand  are three byte  instruction. They  need three  memory  locations to store  them in memory.

Followings  are some  examples  of three  byte  instructions .

LXI 16 bit

JMP 16 bit  address

CALL 16 bit address

Let  us consider  a jump  instruction JMP 2050H. Now  notice  how this  instruction is stored  in the memory.

Notice that first byte is the operation  code. Second  byte is  the low  order byte of the 16  bit data  address. Third  byte is  the high  order  byte of the  16 bit  data  address.

Note  :Low  order byte  of 16 bit address  is multiplexed  with data  bus  and requires de multiplexing  which requires additional  time. But  high  order  byte of  the address does not  require  de multiplexing  therefore  we write  low order byte  first. The  de multiplexing  is already  discussed in cahpter2.