Padding a Microcode Control Word
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2005-Feb-02
Described is a mechanism whereby a Horizontal Microcode control word can specify the state of high-order bits to be used in halfword or fullword ALU (Arithmetic Logic Unit) operations when only an 8-bit immediate field is used. An IA (Immediate Arithmetic) HMC (Horizontal Microcode) control word has 8 bits of immediate information which is used to fully specify the low 8 bits of data in either byte, halfword or fullword mode. It (Image Omitted) also uses one additional pad. This bit specifies the value to be used for the high byte when in halfword mode and the high three bytes when in fullword mode. When this bit is zero, the high byte or high three bytes of ALU input are forced to zero. In like manner, when this bit is one, all of the bits of the high byte(s) of ALU input are forced one.