Toshiba TLCS-870/C1 Series, Manual

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Page 272
18. Serial Bus Interface (SBI)
18.4 Functions
TMP89FM42
RA001
Figure 18-8 Example of Clock Synchronization
As Master 1 pulls down the SCL pin to the low level at point "a", the SCL line of the bus becomes the
low level. After detecting this situation, Master 2 resets counting a clock pulse in the high level and sets
the SCL pin to the low level.
Master 1 finishes counting a clock pulse in the low level at point "b" and sets the SCL pin to the high
level. Since Master 2 holds the SCL line of the bus at the low level, Master 1 waits for counting a clock
pulse in the high level. After Master 2 sets a clock pulse to the high level at point "c" and detects the SCL
line of the bus at the high level, Master 1 starts counting a clock pulse in the high level. Then, the master,
which has finished the counting a clock pulse in the high level, pulls down the SCL pin to the low level.
The clock pulse on the bus is determined by the master device with the shortest high-level period and
the master device with the longest low-level period from among those master devices connected to the
bus.
18.4.5 Master/slave selection
To set a master device, SBI0CR2<MST> should be set to "1".
To set a slave device, SBI0CR2<MST> should be cleared to "0". When a stop condition on the bus or an
arbitration lost is detected, SBI0CR2<MST> is cleared to "0" by the hardware.
18.4.6 Transmitter/receiver selection
To set the device as a transmitter, SBI0CR2<TRX> should be set to "1". To set the device as a receiver,
SBI0CR2<TRX> should be cleared to "0".
For the I
2
C bus data transfer in the slave mode, SBI0CR2<TRX> is set to "1" by the hardware if the direction
bit (R/
W
) sent from the master device is "1", and is cleared to "0" if the bit is "0".
In the master mode, after an acknowledge signal is returned from the slave device, SBI0CR2<TRX> is
cleared to "0" by hardware if a transmitted direction bit is "1", and is set to "1" by hardware if it is "0". When
an acknowledge signal is not returned, the current condition is maintained.
When a stop condition on the bus or an arbitration lost is detected, SBI0CR2<TRX> is cleared to "0" by the
hardware. Table 18-3 shows SBI0CR2<TRX> changing conditions in each mode and SBI0CR2<TRX> value
after changing.
Note:When SBI0CR1<NOACK> is "1", the slave address match detection and the GENERAL CALL detection are
disabled, and thus SBI0CR2<TRX> remains unchanged.
Count start
a b c
SCL pin (Master 1)
SCL pin (Master 2)
SCL (Bus)
Count reset
Wait
Count reset