Datasheet 227
Functional Description
For example, assuming the RTC time is 11 hours: 59 minutes: 59 seconds. When the
external SMBus master reads the hour as 11, then proceeds to read the minute, it is
possible that the rollover happens between the reads and the minute is read as 0. This
results in 11 hours: 0 minute instead of the correct time of 12 hours: 0 minutes. Unless
it is certain that rollover will not occur, software is required to detect the possible time
rollover by reading multiple times such that the read time bytes can be adjusted
accordingly if needed.
5.20.7.4 Format of Host Notify Command
The PCH tracks and responds to the standard Host Notify command as specified in the
System Management Bus (SMBus) Specification, Version 2.0. The host address for this
command is fixed to 0001000b. If the PCH already has data for a previously-received
host notify command which has not been serviced yet by the host software (as
indicated by the HOST_NOTIFY_STS bit), then it will NACK following the host address
byte of the protocol. This allows the host to communicate non-acceptance to the
master and retain the host notify address and data values for the previous cycle until
host software completely services the interrupt.
Note: Host software must always clear the HOST_NOTIFY_STS bit after completing any
necessary reads of the address and data registers.
Table 5-52 shows the Host Notify format.
Table 5-52. Host Notify Format
Bit Description Driven By Comment
1 Start External Master
8:2 SMB Host Address – 7 bits External Master Always 0001_000
9 Write External Master Always 0
10 ACK (or NACK) PCH PCH NACKs if HOST_NOTIFY_STS is 1
17:11 Device Address – 7 bits External Master
Indicates the address of the master;
loaded into the Notify Device Address
Register
18 Unused – Always 0 External Master
7-bit-only address; this bit is inserted
to complete the byte
19 ACK PCH
27:20 Data Byte Low – 8 bits External Master
Loaded into the Notify Data Low Byte
Register
28 ACK PCH
36:29 Data Byte High – 8 bits External Master
Loaded into the Notify Data High Byte
Register
37 ACK PCH
38 Stop External Master
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