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Checking Microprogram Conditional Branches

IP.com Disclosure Number: IPCOM000092033D
Original Publication Date: 1968-Aug-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 22K

Publishing Venue

IBM

Related People

Thomas, J: AUTHOR

Abstract

A comprehensive check on branching within read-only storage ROS is provided by additional ROS fields and logic to duplicate the condition sensing. For each condition branch field that controls ROS sequencing, a check field and a check value are provided. These fields refer to the branching parameter BP and to the branch condition BC specified in the previous microinstruction. In the example shown, microinstruction A specifies a branch to microinstruction C if W=0. If the condition is not met, microinstruction B is to be selected.

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Checking Microprogram Conditional Branches

A comprehensive check on branching within read-only storage ROS is provided by additional ROS fields and logic to duplicate the condition sensing. For each condition branch field that controls ROS sequencing, a check field and a check value are provided. These fields refer to the branching parameter BP and to the branch condition BC specified in the previous microinstruction. In the example shown, microinstruction A specifies a branch to microinstruction C if W=0. If the condition is not met, microinstruction B is to be selected.

The check field of microinstruction B specifies the previous BP, W=0. Because microinstruction B should be reached only if BC is not satisfied, the check value indicates BC=O. The check field of microinstruction C contains the same BP, W=0. The check value for microinstruction C is BC=1. The checking logic is satisfied if microinstruction B is selected and W is nonzero on the previous cycle, or if microinstruction C is selected and W equals zero on the previous cycle.

An alternative implementation eliminates the check field and check value and utilizes a backup, delayed, ROS data register ROSDR to retain the condition branch in a particular microinstruction for an additional cycle permitting the condition branch to be used as the check field in the following cycle. After the conditional branch instruction is executed, ROSDR contains the data that is necessary for the duplicate condition sensing...