XIO3130_0808 Datasheet, PDF (27/139 Pages) Texas Instruments – XIO3130 switch is a PCI Express ´1 3-port fanout switch

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XIO3130
SLLS693D – MAY 2007 – REVISED AUGUST 2008
Figure 3-5. Serial-Bus Start/Stop Conditions and Bit Transfers
Data is transferred serially in 8-bit bytes. During a data transfer operation, an unlimited number of bytes
are transmitted. However, each byte must be followed by an acknowledge bit to continue the data transfer
operation. An acknowledge (ACK) is indicated by the data byte receiver pulling the SDA signal low, so that
it remains low during the high state of the SCL signal. Figure 3-6 illustrates the acknowledge protocol.
Figure 3-6. Serial-Bus Protocol Acknowledge
The XIO3130 performs three basic serial bus operations: single-byte reads, single-byte writes, and
multiple-byte reads. The single-byte operations occur under software control. The multiple-byte read
operations are performed by the serial EEPROM initialization circuitry immediately after a PCI Express
Reset. For details on how the XIO3130 automatically loads the subsystem identification and other register
defaults from the serial-bus EEPROM, see Section 3.4.3, Serial Bus EEPROM Application.
Figure 3-7 illustrates a single-byte write. The XIO3130 issues a start condition and sends the 7-bit slave
device address and the R/W command bit equal to zero. A zero in the R/W command bit indicates that the
data transfer is a write. The slave device acknowledges that it recognizes the slave address. If the
XIO3130 receives no acknowledgment, the SB_ERR status bit is set in the serial-bus control and status
register (PCI offset B3h; see Table 4-32). Next, the XIO3130 sends the EEPROM word address, and
another slave acknowledgment is expected. Then the XIO3130 delivers the data byte (MSB first) and
expects a final acknowledgment before issuing the stop condition.
Figure 3-7. Serial-Bus Protocol – Byte Write
Figure 3-8 illustrates a single-byte read. The XIO3130 issues a start condition and sends the 7-bit slave
device address and the R/W command bit equal to zero (write). The slave device acknowledges that it
recognizes the slave address. Next, the XIO3130 sends the EEPROM word address, and another slave
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