UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 437 of 841
NXP Semiconductors
UM10360
Chapter 19: LPC176x/5x I2C0/1/2
Remark: in the remainder of this chapter, when the phrase “own slave address” is used, it
refers to any of the four configured slave addresses after address masking.
19.7.3 Address mask registers, I2MASK0 to I2MASK3
The four mask registers each contain seven active bits (7:1). Any bit in these registers
which is set to ‘1’ will cause an automatic compare on the corresponding bit of the
received address when it is compared to the I2ADRn register associated with that mask
register. In other words, bits in an I2ADRn register which are masked are not taken into
account in determining an address match.
When an address-match interrupt occurs, the processor will have to read the data register
(I2DAT) to determine which received address actually caused the match.
19.7.4 Comparator
The comparator compares the received 7-bit slave address with any of the four configured
slave addresses in I2ADR0 through I2ADR3 after masking. It also compares the first
received 8-bit byte with the General Call address (0x00). If an a match is found, the
appropriate status bits are set and an interrupt is requested.
19.7.5 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 to be
transmitted is the MSB (bit 7) and, after a byte has been received, the first bit of received
data is located 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.
19.7.6 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 will continue to output clock
pulses (on SCL) until transmission of the current serial byte is complete.
Arbitration may 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.
Figure 91
shows the arbitration procedure.
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