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Microcoded Branch and Link on Count Condition

IP.com Disclosure Number: IPCOM000075532D
Original Publication Date: 1971-Oct-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Anderson, JL: AUTHOR [+3]

Abstract

A number of advantages derive from the use of Branch and Link On Count Match (BLCM) microinstruction words in microprogrammed data processing systems. Appropriate usage permits elimination of "return" or "linking" microinstruction words thereby conserving word storage space in control storage. The compactness in length of the BLCM words also permits conservative but effective usage to be made of bit storage space in control storage.

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Microcoded Branch and Link on Count Condition

A number of advantages derive from the use of Branch and Link On Count Match (BLCM) microinstruction words in microprogrammed data processing systems. Appropriate usage permits elimination of "return" or "linking" microinstruction words thereby conserving word storage space in control storage. The compactness in length of the BLCM words also permits conservative but effective usage to be made of bit storage space in control storage.

In a system organized to utilize 27-bit microinstruction words BLCM, would be coded as follows: Bits 0-5 = Op Code (BLCM) " 6-18 = Branch Address " 19- 26 = Count Field ("link" condition).

Functions associated with the decoding of the BLCM Op Code (operation code) include:
1) Save current (incremented) control store address in saving

register reserved for such use.
2) Save BLCM Count Field (Bits 19-26) in counting unit reserved

for such use and described below.
3) Utilize BLCM Branch Address field (Bits 6-18) as current

control store address.
4) Set a BLCM latch indication.

Beginning with the microinstruction designated by the BLCM Branch Address field, microinstructions are executed successively in normal sequence while the BLCM Counting Unit performs unit counting and condition examining operations. Upon detection of a reference condition in the examination (e.g. zero count if the BLCM Count Field is unit decremented in each control cycle or matching count if the BLCM count field is compared to a count derived by incrementing an initially zero quantity in each control cycle) an uncon...