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Optimal Tab Selection for Placement of Modules

IP.com Disclosure Number: IPCOM000081020D
Original Publication Date: 1974-Mar-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Atkins, JD: AUTHOR

Abstract

A major consideration in the layouts of modules on a board (VTL program) is the wiring of tab connections. In general, if two points are to be connected on a logic card, the probability of the connection being wired increases as the distance between the points, or the wire length, decreases. Repartitioning uses this concept to enhance the wirability of tab connections.

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Optimal Tab Selection for Placement of Modules

A major consideration in the layouts of modules on a board (VTL program) is the wiring of tab connections. In general, if two points are to be connected on a logic card, the probability of the connection being wired increases as the distance between the points, or the wire length, decreases. Repartitioning uses this concept to enhance the wirability of tab connections.

A tab connection is a wire between a pin on a vendor transistor logic (VTL) module and a tab pin. All the tab pins on a standard VTL card are at the bottom of the logic card. The tab pin; are fixed; thus to decrease the wire length of the tab connections, the pins on the VTL modules must be moved as close as possible to the bottom of the logic card. Ideally, all the VTL modules with pins involved in a tab connection might be placed on the bottom row, adjacent to the tab pins. But it is not uncommon for 75% or more of the modules on a VTL logic card to be involved in nets requiring tab connections. To improve the wirability of tab connections, it is necessary to determine a minimum set of modules requiring tab connections. This minimum set of tab modules can then be placed adjacent to the rows of tab pins, if the number of modules in the set can be placed on one row of the logic card. If the minimum set of tab modules exceeds this number, the modules with the fewest number of required tab connections will be placed one row away.

Physical alteration of the net list may be performed to determine the minimum set of tab modules. The nets may be changed by exchanging logically identical portions between VTL modules that have the same part number. This permits the grouping (on the same module) of portions requiring tab connections. The net list is modified because the nets involving the exchanged portions now consist of different pins, but logically the nets remain unchanged. The placement function then places the minimum set of tab modules as close to the tab pins as possible. This reduces the wire lengths required to wire the tab connections and enhances their wirability.

Tab module set minimization is part of Phase 1 of repartitioning. The placement function of the VTL program is performed following the completion of Phase 1 of repartitioning. Definition of a minimum set of tab modules provides a starting point for the placement algorithm. Selection of a cluster of components for placement on a VTL logic card, is based on the potential wiring requirements from a cluster to the VTL card as currently placed. During the initial phase of placement, no components have been placed on the logic card. The only wiring potential during this phase consists of tab wires. Thus, the cluster with the greatest potential tab wiring will be placed first and nearest to the row of tab connectors at the bottom of the card.

The algorithm to select the minimum set of tab modules consist...