PCA9564 datasheet(16/32 Pages) PHILIPS

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Philips Semiconductors

Product data sheet

PCA9564

Parallel bus to I2C-bus controller

2006 Sep 01

STA FLAG

TIME OUT

SDA LINE

SCL LINE

START CONDITION

SU00976

Figure 7. Forced access to a busy I2C-bus

• I2C BUS OBSTRUCTED BY A LOW LEVEL ON SCL OR SDA

An I2C-bus hang-up occurs if SDA or SCL is pulled LOW by an

uncontrolled source. If the SCL line is obstructed (pulled LOW) by a

device on the bus, no further serial transfer is possible, and the SIO

hardware cannot resolve this type of problem. When this occurs, the

problem must be resolved by the device that is pulling the SCL bus

line LOW.

When the SCL line stays LOW for a period equal to the time-out

value, the ’64 concludes that this is a bus error and behaves in a

manner described on page 5 under “Time-out Register”.

If the SDA line is obstructed by another device on the bus (e.g., a

slave device out of bit synchronization), the problem can be solved

by transmitting additional clock pulses on the SCL line (see

Figure 8). The SIO hardware sends out nine clock pulses followed

by the STOP condition. If the SDA line is released by the slave

pulling it LOW, a normal START condition is transmitted by the SIO,

state 08H is entered and the serial transfer continues. If the SDA

line is not released by the slave pulling it LOW, then the SIO

concludes that there is a bus error, loads 70H in I2CSTA, generates

an interrupt signal, and releases the SCL and SDA lines. After the

microcontroller reads the status register, it needs to send an

external reset signal in order to reset the SIO.

If a forced bus access occurs or a repeated START condition is

transmitted while SDA is obstructed (pulled LOW), the SIO

hardware performs the same action as described above. In each

case, state 08H is entered after a successful START condition is

transmitted and normal serial transfer continues. Note that the CPU

is not involved in solving these bus hang-up problems.

• BUS ERROR

A bus error occurs when a START or STOP condition is present at

an illegal position in the format frame. Examples of illegal positions

are during the serial transfer of an address byte, a data or an

acknowledge bit.

The SIO hardware only reacts to a bus error when it is involved in a

serial transfer either as a master or an addressed slave. When a

bus error is detected, SIO releases the SDA and SCL lines, sets the

interrupt flag, and loads the status register with 00H. This status

code may be used to vector to a service routine which either

attempts the aborted serial transfer again or simply recovers from

the error condition as shown in Table 6. The microcontroller must

send an external reset signal to reset the SIO.

STA FLAG

SDA LINE

SCL LINE

su01663

START

CONDITION

STOP

CONDITION

Figure 8. Recovering from a bus obstruction caused by a LOW level on SDA

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