XIO2001IPNP datasheet(37/144 Pages) TI

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SCL From

Master

SDA Output

By Transmitter

SDA Output

By Receiver

XIO2001

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SCPS212I – MAY 2009 – REVISED JANUARY 2016

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Figure 20. Serial-Bus Protocol Acknowledge

The bridge performs three basic serial-bus operations: single byte reads, single byte writes, and multibyte reads.

The single byte operations occur under software control. The multibyte read operations are performed by the

serial EEPROM initialization circuitry immediately after a PCI Express reset. See Serial-Bus EEPROM

Application, Serial-Bus EEPROM Application, for details on how the bridge automatically loads the subsystem

identification and other register defaults from the serial-bus EEPROM.

Figure 21 illustrates a single byte write. The bridge issues a start condition and sends the 7-bit slave device

address and the R/W command bit is equal to 0b. A 0b in the R/W command bit indicates that the data transfer is

a write. The slave device acknowledges if it recognizes the slave address. If no acknowledgment is received by

the bridge, then bit 1 (SB_ERR) is set in the serial-bus control and status register (PCI offset B3h, see Serial-Bus

Control and Status Register). Next, the EEPROM word address is sent by the bridge, and another slave

acknowledgment is expected. Then the bridge delivers the data byte MSB first and expects a final

acknowledgment before issuing the stop condition.

Figure 21. Serial-Bus Protocol – Byte Write

Figure 22 illustrates a single byte read. The bridge issues a start condition and sends the 7-bit slave device

address and the R/W command bit is equal to 0b (write). The slave device acknowledges if it recognizes the

slave address. Next, the EEPROM word address is sent by the bridge, and another slave acknowledgment is

expected. Then, the bridge issues a restart condition followed by the 7-bit slave address and the R/W command

bit is equal to 1b (read). Once again, the slave device responds with an acknowledge. Next, the slave device

sends the 8-bit data byte, MSB first. Since this is a 1-byte read, the bridge responds with no acknowledge (logic

high) indicating the last data byte. Finally, the bridge issues a stop condition.

Figure 22. Serial-Bus Protocol – Byte Read

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