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Condition Code for Minicomputer

IP.com Disclosure Number: IPCOM000085837D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Kuhne, R: AUTHOR [+2]

Abstract

Computers are generally provided with an ALU fed with two operands A and B stored into two stacks of registers (see SA and SB in the figure). The arithmetical or logical operation performed on A and B into the ALU is defined by the program under execution. But also branches on the program may have to be determined by testing one bit position of A or B. The result of the test will then provide a branch code condition. Means are provided here for performing the test and getting the branch code with very little additional hardware.

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Condition Code for Minicomputer

Computers are generally provided with an ALU fed with two operands A and B stored into two stacks of registers (see SA and SB in the figure). The arithmetical or logical operation performed on A and B into the ALU is defined by the program under execution. But also branches on the program may have to be determined by testing one bit position of A or B. The result of the test will then provide a branch code condition. Means are provided here for performing the test and getting the branch code with very little additional hardware.

Let the branch condition depend on the value of a given bit position of an operand A (due to the symmetry of the system anything performed on A could also be performed on B). Two situations may generally occur depending on whether the bit position should either be set or reset after the test. Both cases on an example will be examined.

Suppose that the th bit position of A has to be tested. Then A may either be A = x x 1 x x x x x P or x x o x x x x x P, P being the parity bit. For performing the Test and Set, define a mask M = 0 0 1 0 0 0 0 0 0 and perform an OR function. TEST AND SET : two cases are possible: A = x x 1 x x x x x P M = 0 0 1 0 0 0 0 0 0 (A) OR (M) = x x 1 x x x x x P or; A = x x 1 x x x x x P M = 0 0 1 0 0 0 0 0 0
(A) or (M) = x x 1 x x x x x P The system being in fact provided with parity check generators, the ALU will provide x x 1 x x x x x P. Now perform the Test And Reset function usin...