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Condition Code Setting Hardware

IP.com Disclosure Number: IPCOM000085797D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Bechdel, JF: AUTHOR [+2]

Abstract

In a microprogrammed data processor, a series of microcode steps are required to determine the condition code (CC) setting for the TEST UNDER MASK (TM) machine instruction. The hardware described herein automatically determines the condition code setting for this type of instruction. This enables a significant reduction in overall instruction execution time.

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Condition Code Setting Hardware

In a microprogrammed data processor, a series of microcode steps are required to determine the condition code (CC) setting for the TEST UNDER MASK (TM) machine instruction. The hardware described herein automatically determines the condition code setting for this type of instruction. This enables a significant reduction in overall instruction execution time.

The TEST UNDER MASK instruction is of the storage-immediate (SI) type shown in Fig. 1. The "immediate" byte of data (bits 8-15) is used as an eight-bit mask. The mask bits correspond one-for-one with the eight bits in the storage location specified by the first operand address (bits 16-31) in the instruction. A mask bit of one indicates the respective bit in storage is to be tested. When the mask bit is 0, the storage bit is ignored. When all storage bits selected are 0 or if the mask is all 0's, the condition code (CC) is set to Omega. When the selected bits are all 1's, the condition code is set to three. Any other combination (mixed) results in a condition code of one.

The hardware for determining the proper condition code includes two identical 256 x 2 read-only storage (ROS) arrays 10 and 12 for performing table- up functions. The logic performed by ROS 10 is indicated in Fig. 2. The X1 and Y1 outputs as a function of the applied address pattern are:

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The X1 output is active only if all selected test bits are 1's.

The Y1 output is active only when all select...