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47.4.2.1 Master-transmitter addresses a slave-receiver
The transfer direction is not changed. When a 10-bit address follows a START condition,
each slave compares the first 7 bits of the first byte of the slave address (11110XX) with
its own address and tests whether the eighth bit (R/W direction bit) is 0. It is possible that
more than one device finds a match and generates an acknowledge (A1). Each slave that
finds a match compares the 8 bits of the second byte of the slave address with its own
address, but only one slave finds a match and generates an acknowledge (A2). The
matching slave remains addressed by the master until it receives a STOP condition (P) or
a repeated START condition (Sr) followed by a different slave address.
Table 47-42. Master-transmitter addresses slave-receiver with a 10-bit
address
S
Slave
address
first 7 bits
11110 +
AD10 +
AD9
R/W
0
A1
Slave
address
second
byte
AD[8:1]
A2 Data A ... Data A/A P
After the master-transmitter has sent the first byte of the 10-bit address, the slave-receiver
sees an I2C interrupt. User software must ensure that for this interrupt, the contents of the
Data register are ignored and not treated as valid data.
47.4.2.2 Master-receiver addresses a slave-transmitter
The transfer direction is changed after the second R/W bit. Up to and including
acknowledge bit A2, the procedure is the same as that described for a master-transmitter
addressing a slave-receiver. After the repeated START condition (Sr), a matching slave
remembers that it was addressed before. This slave then checks whether the first seven
bits of the first byte of the slave address following Sr are the same as they were after the
START condition (S), and it tests whether the eighth (R/W) bit is 1. If there is a match,
the slave considers that it has been addressed as a transmitter and generates acknowledge
A3. The slave-transmitter remains addressed until it receives a STOP condition (P) or a
repeated START condition (Sr) followed by a different slave address.
After a repeated START condition (Sr), all other slave devices also compare the first
seven bits of the first byte of the slave address with their own addresses and test the
eighth (R/
W) bit. However, none of them are addressed because R/W = 1 (for 10-bit
devices), or the 11110XX slave address (for 7-bit devices) does not match.
Chapter 47 Inter-Integrated Circuit (I2C)
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Freescale Semiconductor, Inc.
Preliminary
1253
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