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23614K—October 2003 AMD Athlon™ Processor Model 4 Revision Guide
Preliminary Information
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.)