AMD 26029 free download

File name 26029.pdf

Confidential - Advance Information Date: February 8, 2002 Technical Note: 26029 0.2 CPG Technical Marketing FSB_Sense Circuitry Abstract: This technical note is intended for AMD motherboard partners developing products based on mobile AMD AthlonTM and AMD DuronTM processors model 8 and higher. This document describes the motherboard circuitry required to automatically determine the Front Side Bus (FSB) speed of the processor. This information will be incorporated into the next revision of the AMD AthlonTM Processor-Based Motherboard Design Guide, order# 24363. Problem: Currently mobile motherboards are unable to automatically distinguish between processors that have 100-MHz FSB and those that have a 133-MHz FSB. Solution: Mobile Model 8 and higher processors have a pin named FSB_Sense that when used with the appropriate FSB_Sense circuitry allows the motherboard to distinguish between processors that have a 100-MHz FSB and those that have a 133-MHz FSB. Note: For the exact location of the FSB_Sense Pin refer to the appropriate processor data sheet. Th e l og i c l eve l o f t h e F S B _ S e n s e p i n c a n b e u s e d t o automatically configure the frequency strapping of the system clock generator and Northbridge. Most clock generators currently being used have the capability of selecting between 100-MHz and 133-MHz FSB frequencies by manipulating a single Frequency Select strap that is latched by the clock generator shortly after it powers up. For the Northbridge frequency strapping, there may be one or two straps that must be manipulated as it powers up. The logic level of the FSB_Sense signal from the CPU will typically need to be inverted to match the logic level of the clock generator and Northbridge strap inputs. The FSB_Sense pin will have an open circuit connection for mobile processors wit