Datasheet
Feature/Protocol Descriptions
29
March 5 2007 − June 2011 SCPS154C
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 3−7 illustrates an example application implementing the two-wire serial bus.
GPIO4 // SCL
GPIO5 // SDA
V
DD_33
A0
A1
A2
SCL
SDA
XIO2200A
Serial
EEPROM
Figure 3−7. Serial EEPROM Application
3.6.2 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 3−8. 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 3−8. 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.
SDA
SCL
Start
Condition
Stop
Condition
Change of
Data Allowed
Data Line Stable,
Data Valid
Figure 3−8. 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 3−9 illustrates the acknowledge protocol.
Not Recommended for New Designs