Resistance Value of the ZN and ZP Pins

Preliminary Information

23614K— October 2003

AMD Athlon™ Processor Model 4 Revision Guide

10 Resistance Value of the ZN and ZP Pins

Products Affected. A4, A5

Normal Specified Operation. The ZN and ZP pins are specified such that the AMD system bus output drivers autocompensate to whatever resistance value is applied between ZN and VDD and ZP and VSS.

Non-conformance.The AMD system bus driver impedance is approximately 20 ohms higher than the applied resistor value.

Potential Effect on System. The AMD Athlon system bus signal quality for signals driven to the Northbridge may be adversely affected.

Suggested Workaround. All motherboards should have ZN/ZP resistors set to approximately 20 ohms less than the characteristic board impedance.

Resolution Status. Fix planned for a future revision.

Note: When future revisions of the processor are used with motherboards implementing the workaround, the expected output impedance of the driver will continue to yield good signal quality. (For example, with a motherboard setting of 40 ohms for ZN and ZP, an old part that drives with a 60-ohm driver works properly. A revised part with a true 40-ohm driver also works properly.)