مدارهای هازارد

مدارهای هازارد

اسلاید 1: Hazard

اسلاید 2: 2شکل موج هاتا به حال تاخير گيت ها در نظر گرفته نمي شدند:تاخير صفر: غير واقعييا علاقه به دانستن رفتار حالت پايدارفرض: ورودي ها براي مدت طولاني (نسبت به تاخيرالمان هاي مدار) پايدار بوده اند.ABF=A•BG=A+BH=A’1111100000t0t1t2t3t4t5t6

اسلاید 3: 3تاخيرتاخير در مدارها

اسلاید 4: 4تاخيرهاInertial DelayTransport Delay

اسلاید 5: 5شکل موج هاxyzF11110000t0t1t2t3t4t5t6

اسلاید 6: 6Hazardتاخيرها ممکن است باعث پالس هاي ناخواسته شوندGlitchهازارد:مداري که احتمال ايجاد glitch در آن هست، هازارد دارد.دو نوع:استاتيکديناميک

اسلاید 7: 7مثالInitially: X=Y=Z=1

اسلاید 8: 8Static HazardDefinition:A static-1 hazard is the possibility of a 0 glitch when we expect the output to remain at a nice steady 1 based on a static analysisFormal Definition:A static-1 hazard is a pair of input combinations that: (a) differ in only one input variable and(b) both give a 1 output; such that it is possible for a momentary 0 output to occur during a transition in the differing input variable.

اسلاید 9: 9مثالEven though “static” analysis predicts that the output is 1 for both input combinations X,Y,Z = 111 and X,Y,Z = 110,F goes to 0 for one unit time.

اسلاید 10: 10Static-0 HazardA properly designed two-level sum-of-products (AND-OR) circuit has no static-0 hazards.A static-0 hazard is just the dual of a static-1 hazard an OR-AND circuit that is the dual of the example circuit would have a static-0 hazard.

اسلاید 11: 11مثالتحليل کنيد:

اسلاید 12: 12تشخيص هازاردA Karnaugh map can be used to detect static hazards in a two-level SOP or POS circuit.

اسلاید 13: 13رفع هازارد

اسلاید 14: 14مثال

اسلاید 15: 15Dynamic HazardDynamic hazard:the possibility of an output changing more than once as the result of a single input transition.Multiple output transitions can occur if there are multiple paths with different delays from the changing input to the changing output.

اسلاید 16: 16مثالسه مسير از X به FW,X,Y,Z = 0,0,0,1  F=1فرض: X يک شود.فرض: بقية گيت ها سريعند.اول تغييرات مشکي  F=0بعد آبي غير ايتاليکبعد آبي ايتاليک

اسلاید 17: 17طراحي مدار بدون هازاردTechniques for finding hazards in arbitrary circuits, are rather difficult to use. when you require a hazard-free design, it’s best to use a circuit structure that is easy to analyze.In particular, two-level AND-OR circuit has no static-0 or dynamic hazards. Static-1 hazards may exist in such a circuit but they can be found and eliminated using K-map.

اسلاید 18: 18نکتهMost Hazards are not hazardous:A well-designed, synchronous digital system is structured so that hazard analysis is not needed for most of its circuits. In a synchronous system, all of the inputs to a combinational circuit are changed at a particular time, and the outputs are not “looked at” until they have had time to settle to a steady-state value. Hazard analysis and elimination are typically needed only in the design of asynchronous sequential circuits,Asynchronous circuits are not the mainstream but if you want to design them, an understanding of hazards will be absolutely essential for a reliable result.

اسلاید 19: 19Pulse-Shaping CircuitA ·A = 0F is not always 0!3 gate delaysD remains high forthree gate delays afterA changes from low to highABFCD