NXP Semiconductors PCA9665 8.9 Some special cases

Product data sheet Rev. 02 — 7 December 2006 58 of 91

NXP Semiconductors PCA9665

Fm+ parallel bus to I2C-bus controller

This status code indicates that the SCL line is stuck LOW.

8.9 Some special cases

The PCA9665 has facilities to handle the following special cases that may occur during a

serial transfer.

A repeated START condition may be generated in the Master Transmitter or Master

Receiver modes. A special case occurs if another master simultaneously generates a

repeated START condition (seeFigure 15). Until this occurs, arbitration is not lost by

either master since they were both transmitting the same data.

If the PCA9665 detects a repeated START condition on the I2C-bus before generating a

repeated START condition itself, it will use the repeated START as its own and continue

with the sending of the slave address.

Arbitration may be lost in the Master Transmitter and Master Receiver modes. Loss of

arbitrationis indicated by the following states in I2CSTA; 38h, 68h, and B0h (see Figure 7,

Figure 11,Figure 8, and Figure 12).

Remark: In order to exit state 38h, a Time-out, Reset, or external STOP are required.

Ifthe STA ﬂag in I2CCON is set by the routines which service these states, then, if the bus

is free again, a START condition (state 08h) is transmitted without intervention by the

CPU, and a retry of the total serial transfer can commence.

8.9.3 Forced access to the I2C-bus

In some applications, it may be possible for an uncontrolled source to cause a bus

hang-up. In such situations, the problem may be caused by interference, temporary

interruption of the bus or a temporary short-circuit between SDA and SCL.

If an uncontrolled source generates a superﬂuous START or masks a STOP condition,

then the I2C-bus stays busy indeﬁnitely. If the STA ﬂag is set and bus access is not

obtained within a reasonable amount of time, then a forced access to the I2C-bus is

possible. If the I2C-bus stays idle for a time period equal to the time-out period, then the

PCA9665 concludes that no other master is using the bus and sends a START condition.

Fig 15. Simultaneous repeated START conditions from 2 masters

S SLA W A DATA A

18h 28h

002aab028

other master sends

repeated START condition earlier

08h

Sboth masters continue

with SLA transmission