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Rev. 1.00, 05/04, page 346 of 544
13. Note on ICDR read in transmit mode and ICDR write in receive mode
If ICDR is read in transmit mode (TRS = 1) or ICDR is written to in receive mode (TRS = 0),
the SCL pin may not be held low in some cases after transmit/receive operation has been
completed, thus inconveniently allowing clock pulses to be output on the SCL bus line before
ICDR is accessed correctly. To access ICDR correctly, read ICDR after setting receive mode
or write to ICDR after setting transmit mode.
14. Note on ACKE and TRS bits in slave mode
In the I
2
C bus interface, if 1 is received as the acknowledge bit value (ACKB = 1) in transmit
mode (TRS = 1) and then the address is received in slave mode without performing appropriate
processing, interrupt handling may start at the rising edge of the 9th clock pulse even when the
address does not match. Similarly, if the start condition or address is transmitted from the
master device in slave transmit mode (TRS = 1), the IRIC flag may be set after the ICDRE flag
is set and 1 received as the acknowledge bit value (ACKB = 1), thus causing an interrupt
source even when the address does not match.
To use the I
2
C bus interface module in slave mode, be sure to follow the procedures below.
A. When having received 1 as the acknowledge bit value for the last transmit data at the end
of a series of transmit operation, clear the ACKE bit in ICCR once to initialize the ACKB
bit to 0.
B. Set receive mode (TRS = 0) before the next start condition is input in slave mode.
Complete transmit operation by the procedure shown in figure 13.23, in order to switch
from slave transmit mode to slave receive mode.
15. Note on Arbitration Lost in Master Mode
The I
2
C bus interface recognizes the data in transmit/receive frame as an address when
arbitration is lost in master mode and a transition to slave receive mode is automatically
carried out.
When arbitration is lost not in the first frame but in the second frame or subsequent frame,
transmit/receive data that is not an address is compared with the value set in the SAR or SARX
register as an address. If the receive data matches with the address in the SAR or SARX
register, the I
2
C bus interface erroneously recognizes that the address call has occurred. (See
figure 13.35.)
In multi-master mode, a bus conflict could happen. When the I
2
C bus interface is operated in
master mode, check the state of the AL bit in the ICSR register every time after one frame of
data has been transmitted or received.
When arbitration is lost during transmitting the second frame or subsequent frame, take
avoidance measures.