XIO2001_16 Datasheet, PDF (36/141 Pages) Texas Instruments – PCI Express to PCI Bus Translation Bridge

XIO2001
SCPS212I – MAY 2009 – REVISED JANUARY 2016
www.ti.com
The bridge implements a two-terminal serial interface with one clock signal (SCL) and one data signal (SDA).
The SCL signal is a unidirectional output from the bridge and the SDA signal is bidirectional. Both are open-drain
signals and require pullup resistors. The bridge is a bus master device and drives SCL at approximately 60 kHz
during data transfers and places SCL in a high-impedance state (0 frequency) during bus idle states. The serial
EEPROM is a bus slave device and must acknowledge a slave address equal to A0h. Figure 18 illustrates an
example application implementing the two-wire serial bus.
VDD_33
Serial
EEPROM
A0
A1 SCL
A2 SDA
XIO2001
GPIO4 // SCL
GPIO3 // SDA
Figure 18. Serial EEPROM Application
8.3.8.2 Serial-Bus Interface Protocol
All data transfers are initiated by the serial-bus master. The beginning of a data transfer is indicated by a start
condition, which is signaled when the SDA line transitions to the low state while SCL is in the high state, as
illustrated in Figure 19. The end of a requested data transfer is indicated by a stop condition, which is signaled
by a low-to-high transition of SDA while SCL is in the high state, as shown in Figure 19. Data on SDA must
remain stable during the high state of the SCL signal, as changes on the SDA signal during the high state of SCL
are interpreted as control signals, that is, a start or stop condition.
Figure 19. Serial-Bus Start/Stop Conditions and Bit Transfers
Data is transferred serially in 8-bit bytes. During a data transfer operation, the exact number of bytes that are
transmitted is unlimited. 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 20 illustrates the acknowledge protocol.
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