circles are used to indicate when the serial interrupt flag is set. A serial interrupt is not
generated when I2CSTA = F8h. This happens on a STOP condition or when an external
reset is generated (at power-up, when RESET pin is going LOW or during a software reset
on the parallel bus). The numbers in the circles show the status code held in the I2CSTA
register. At these points, a service routine must be executed to continue or complete the
serial transfer. These service routines are not critical since the serial transfer is
suspended until the serial interrupt flag is cleared by software.

When a serial interrupt routine is entered, the status code in I2CSTA is used to branch to
the appropriate service routine. For each status code, the required software action and
details of the following serial transfer are given in

Table 27

Table 28

Table 31

8.3 Byte mode

8.3.1 Master Transmitter Byte mode

In the Master Transmitter Byte mode, a number of data bytes are transmitted to a slave
receiver (see

Figure 7

). Before the Master Transmitter Byte mode can be entered,

I2CCON must be initialized as shown in

Table 26

ENSIO must be set to logic 1 to enable the PCA9665. If the AA bit is reset, the PCA9665
will not acknowledge its own slave address in the event of another device becoming
master of the bus. (In other words, if AA is reset, PCA9665 cannot enter a slave mode.)
STA, STO, and SI must be reset. Once ENSIO has been set to 1, it takes about 550

s for

the oscillator to start up.

The Master Transmitter Byte mode may now be entered by setting the STA bit. The
I

C-bus state machine will first test the I

C-bus and generate a START condition as soon

as the bus becomes free. When a START condition is transmitted, the serial interrupt flag
(SI) is set, the Interrupt line (INT) goes LOW and the status code in the status register
(I2CSTA) will be 08h. This status code must be used to vector to an interrupt service
routine that loads I2CDAT with the slave address and the data direction bit (SLA+W). A
write to I2CCON resets the SI bit, clears the Interrupt (INT goes HIGH) and allows the
serial transfer to continue.

When the slave address with the direction bit have been transmitted, the Serial Interrupt
flag (SI) is set again, the Interrupt line (INT) goes LOW again and I2CSTA is loaded with
the following possible codes:

•

18h if an acknowledgment bit (ACK) has been received

•

20h if an no acknowledgment bit (NACK) has been received

•

38h if the PCA9665 lost the arbitration

Table 26.

I2CCON initialization (Byte mode)

Bit

Symbol

ENSIO

STA

STO

reserved reserved

MODE

Value