Browse Prior Art Database

Trigger Block Simulation

IP.com Disclosure Number: IPCOM000074449D
Original Publication Date: 1971-Apr-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 27K

Publishing Venue

IBM

Related People

Langdon, GG: AUTHOR

Abstract

A three value simulator program can be used for design verification and fault simulation. Basically, a three-valued simulation consists of an X-PASS, where all signals which experience a change are changed to the X state; followed by a V-PASS (Value Pass) where all signals change to a value of 0 or 1.

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Trigger Block Simulation

A three value simulator program can be used for design verification and fault simulation. Basically, a three-valued simulation consists of an X-PASS, where all signals which experience a change are changed to the X state; followed by a V- PASS (Value Pass) where all signals change to a value of 0 or 1.

A problem exists in simulating computer logic when the "logic block" to be simulated is a trigger; this is especially true if the trigger is not clocked. Triggers can be simulated by artificially introducing "unit delay" blocks in conjunction with other logic blocks, where a unit delay block will cause a delayed X-PASS and delayed V-PASS when its input experiences a change.

A list, DList, keeps track of the delay blocks experiencing changes during a pass and an index, DHOLD, keeps track of the number of entries on DLIST. Corresponding to each delay block is a Delay Table entry; each entry keeps track of data corresponding to the unit delay block output in the most recent past.

Two bits are used to denote the three permissible signal values as follows: 11=1, 10=X, 00=0. The general schematic of the block is shown in the sketch.

It is necessary to know the direction in which input signals are changing; therefore a storage area with a function similar to the Delay Tables is required. Also, due to the problem of an input possibly going to X on an XPASS and remaining there for the subsequent VPASS, an index similar to DHOLD and a list like the DLIST is needed. For convenience, let us call these storage areas T- TABLE, T HOLD and T LIST, respectively. The T-TABLE should contain a block of words for each trigger in the machine, one word or slot for each AC input or gate input to the trigger.

The slots are to store the values of the respective signals at the end of the last value pass. The index THOLD and the...