NXP Semiconductors PCA9665 - Manual (Page 58)

PCA9665_2 © NXP B.V. 2006. All rights reserved.
Product data sheet Rev. 02 — 7 December 2006 58 of 91
NXP Semiconductors
PCA9665
Fm+ parallel bus to I 2 C-bus controller
8.8.4 I2CSTA = 78h
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.
8.9.1 Simultaneous repeated START conditions from two masters
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 (see
Figure 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 I 2 C-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.
8.9.2 Data transfer after loss of arbitration
Arbitration may be lost in the Master Transmitter and Master Receiver modes. Loss of
arbitration is 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.
If the 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 I 2 C-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 I
2 C-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 I 2 C-bus is
possible. If the I 2 C-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
S
both masters continue
with SLA transmission