
Advanced Notebook I/O for ISA or LPC Designs
Datasheet
Rev. 0.5 (03-24-05)
Page 38
SMSC SIO10N268
DATASHEET
See the Low Pin Count (LPC) Interface Specification Reference, Section 8.2.
8.3.5.3
SYNC Protocol
See the Low Pin Count (LPC) Interface Specification Reference, Section 4.2.1.8 for a table of valid SYNC
values.
The SYNC pattern is used to add wait states. For read cycles, the SIO10N268 immediately drives the
SYNC pattern upon recognizing the cycle. The host immediately drives the sync pattern for write cycles. If
the SIO10N268 needs to assert wait states, it does so by driving 0101 or 0110 on LAD[3:0] until it is ready,
at which point it will drive 0000 or 1001. The SIO10N268 will choose to assert 0101 or 0110, but not switch
between the two patterns.
The data (or wait state SYNC) will immediately follow the 0000 or 1001 value.
The SYNC value of 0101 is intended to be used for normal wait states, wherein the cycle will complete
within a few clocks. The SIO10N268 uses a SYNC of 0101 for all wait states in a DMA transfer.
The SYNC value of 0110 is intended to be used where the number of wait states is large. This is provided
for EPP cycles, where the number of wait states could be quite large (>1 microsecond). However, the
SIO10N268 uses a SYNC of 0110 for all wait states in an I/O transfer.
The SYNC value is driven within 3 clocks.
8.3.5.4
SYNC Timeout
The SYNC value is driven within 3 clocks. If the host observes 3 consecutive clocks without a valid SYNC
pattern, it will abort the cycle.
The SIO10N268 does not assume any particular timeout. When the host is driving SYNC, it may have to
insert a very large number of wait states, depending on PCI latencies and retries.
8.3.5.5
SYNC Patterns and Maximum Number of SYNCS
If the SYNC pattern is 0101, then the host assumes that the maximum number of SYNCs is 8.
If the SYNC pattern is 0110, then no maximum number of SYNCs is assumed. The SIO10N268 has
protection mechanisms to complete the cycle. This is used for EPP data transfers and will utilize the same
timeout protection that is in EPP.
8.3.5.6
SYNC Error Indication
The SIO10N268 reports errors via the LAD[3:0] = 1010 SYNC encoding.
If the host was reading data from the SIO10N268, data will still be transferred in the next two nibbles. This
data may be invalid, but it will be transferred by the SIO10N268. If the host was writing data to the
SIO10N268, the data had already been transferred.
In the case of multiple byte cycles, such as DMA cycles, an error SYNC terminates the cycle. Therefore, if
the host is transferring 4 bytes from a device, if the device returns the error SYNC in the first byte, the
other three bytes will not be transferred.