6402 datasheet(82/250 Pages) INTEL

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SMBus Interface

Intel® 6400/6402 Advanced Memory Buffer Datasheet

This is not a problem since SMBus accesses are only required prior to initial link turn-on

or for diagnostic access when a link can not be initialized. It is the host’s responsibility

to monitor for SMBus transactions during a fast reset and retry these transactions when

the link is stable.

An interrupted transaction will result in the AMB as slave not properly acknowledging

the Master. This protects write transactions. However, if a read transaction has

proceeded to the point where the slave no longer acknowledges the master, read data

can be lost when the SMBus state machine is reset. If PEC is enabled, this data loss will

be detected as a PEC error.

The host restricting usage of SMBus to when the link is idle or monitoring “fast resets”

and retrying transactions that are interrupted is the safest SMBus access method.

7.1.5.2

SMBus Interface State Machine Reset

The slave interface state machine can be reset by the master in two ways:

• The master holds SCL low for 25 ms cumulative. Cumulative in this case means

that all the “low time” for SCL is counted between the Start and Stop bit. If this

totals 25 ms before reaching the Stop bit, the interface is reset.

— Timing is set up to be:

* 30 ms at DDR2-667

* 37.5 ms at DDR2-533

• The master holds SCL continuously high for 50 µs.

— Timing is set up to be:

* 60 µs at DDR2-667

* 75 µs at DDR2-533

7.1.5.3

SMBus Transactions During Hard Reset

Since the configuration registers are affected by the reset pin, SMBus masters will NOT

be able to access the internal registers while the system is reset.

6402 Datasheet(PDF) 82 Page - Intel Corporation