UM10413
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 1 — 16 December 2011
121 of 268
NXP Semiconductors
UM10413
MPT612 User manual
16.6.2 Address register, I2ADDR
This register can be loaded with the 7-bit slave address (7 most significant bits) to which
the I
2
C block responds when programmed as a slave transmitter or receiver. The LSB
(GC) is used to enable general call address (0x00) recognition.
16.6.3 Comparator
The comparator compares the received 7-bit slave address with its own slave address (7
most significant bits in I2ADR). It also compares the first received 8-bit byte with the
general call address (0x00). If an equality is found, the appropriate status bits are set and
an interrupt is requested.
16.6.4 Shift register, I2DAT
This 8-bit register contains a byte of serial data to be transmitted or a byte which has just
been received. Data in I2DAT is always shifted from right to left; the first bit transmitted is
the MSB (bit 7) and, after a byte is received, the first bit of received data is at the MSB of
I2DAT. While data is being shifted out, data on the bus is simultaneously being shifted in;
I2DAT always contains the last byte present on the bus. Thus, in the event of lost
arbitration, the transition from master transmitter to slave receiver is made with the correct
data in I2DAT.
16.6.5 Arbitration and synchronization logic
In the master transmitter mode, the arbitration logic checks that every transmitted logic 1
actually appears as a logic 1 on the I
2
C-bus. If another device on the bus overrules a
logic 1 and pulls the SDA line LOW, arbitration is lost, and the I
2
C block immediately
changes from master transmitter to slave receiver. The I
2
C block continues to output clock
pulses (on SCL) until transmission of the current serial byte is complete.
Arbitration can also be lost in the master receiver mode. Loss of arbitration in this mode
can only occur while the I
2
C block is returning a “not acknowledge: (logic 1) to the bus.
Arbitration is lost when another device on the bus pulls this signal LOW. Since this can
occur only at the end of a serial byte, the I
2
C block generates no further clock pulses.
shows the arbitration procedure.
(1) Another device transmits serial data.
(2) Another device overrules a logic 1 (dotted line) transmitted by this I
2
C master by pulling the SDA
line LOW. Arbitration is lost, and this I
2
C enters slave receiver mode.
(3) This I
2
C is in slave receiver mode but still generates clock pulses until the current byte is
transmitted. This I
2
C will not generate clock pulses for the next byte. Data on SDA originates from
the new master once it has won arbitration.
Fig 33. Arbitration procedure
SDA line
SCL line
ACK
8
9
3
4
1
(1)
(1)
(2)
(3)
2
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