Shift Instructions, Multiply and Divide

Abstract

Shift instructions allow the bits of a register or memory byte to be shifted one bit place to the left or to the right. There are two types of shift instructions — logical and arithmetic. Logical shifts consider the contents of the register or memory byte to be just a bit pattern when the shift is made. Arithmetic shifts consider the contents of the register or memory byte to be a signed number so that when the shift is made the number is arithmetically multiplied by two (left shift) or divided by two (right shift). The Z80 microprocessor has one logical instruction and two arithmetic instructions. Descriptions of the shift instructions are included in Table C.8 in Appendix C.