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ST92195 ST92T195 ST92E195 - TWO-CHANNEL I2C BUS INTERFACE (I2C)
I2C BUS INTERFACE (Cont’d)
Bit 1 = UNEXP
Unexpected flag bit
This bit is useful for error detection in a multimas-
ter mode system, when a master is continuing its
transaction while an other concurrent master
wants to finish or restart a transaction by sending a
“Start” or a “Stop” condition.
Together with the MISP bit, it covers all possible
cases, where unexpected “Start” or “Stop” condi-
tions occur, while the interface is a master.
0: No Unexpected error detected
1: A master interface receives a “Start” or a “Stop”
condition, while sending the first bit of a data
byte.
Notes:
– If this bit is set, it will automatically activate the
ERROR bit.
– This bit is only valid when the Advanced Fea-
tures Enable bit AFEN is set.
Bit 0 = MISP
Misplaced flag bit
This bit indicates if the interface has received a
misplaced “Start” or “Stop” condition during ad-
dress transfer or any data byte transfer (besides
first data bit). This error detection is also activated
during the acknowledge bit transfer.
Together with the UNEXP bit, it covers all possible
cases, where unexpected “Start” or “Stop” condi-
tions occur, while the interface is a master.
0: No misplaced “start” or “stop” condition has
been detected
1: A misplaced “Start” or “Stop” condition has been
received.
Note: If this bit is set, it will automatically activate
the ERROR bit.
STATUS REGISTER 1 (I2CSTR1)
R245 - Read Only
Register Page: 44
Reset Value: 0000 0000(00h)
Bit 7 = ERROR
ERROR detection bit
This bit indicates if an error occurred on the bus or
not.
0: No error detected
1: An error is detected. It is an illegal start or stop
condition, i.e. a signal level transition occurs on
the SDA bus during presence of a clock pulse
on the SCL bus.
An interrupt is generated in this case. The inter-
face stays in the error state until the error flag is
reset by either a CLEAR operation, a STOP re-
quest or a “Return To Inactive State” operation.
Note: the ERROR bit has higher priority than the
ARB_LOST bit (i.e. when ERROR=1, the value of
ARB_LOST has to be ignored).
70
ERROR
ARB_
LOST
READ FIRST
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ACK_
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ACTIVE