TMP88CS38FG datasheet(95/226 Pages) TOSHIBA

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TMP88CS38/CM38A/CP38A

2007-09-12

88CS38-95

(9) Serial bus interface operating mode selection

The SBIM (Bit3 and 2 in SBICRB) is used to specify a serial bus interface operation

mode.

Set the SBIM to “10” in order to change a operation mode to I2C bus mode. Before

changing operation mode, confirm serial bus interface pins in a high level. And switch

a mode to port after confirming that a bus is free.

(10) Arbitration lost detection monitor

Since more than one master device can exist simultaneously on a bus in the I2C bus

mode, a bus arbitration procedure is implemented in order to guarantee the contents of

transferred data.

Data on the SDA line is used for bus arbitration of the I2C bus.

The following shows an example of a bus arbitration procedure when two master

devices exist simultaneously on a bus. Master 1 and master 2 output the same data

until point “a”. After master 1 outputs “1” and master 2, “0”, the SDA line of a bus is

wired AND and the SDA line is pulled down to the low level by master 2. When the

SCL line of a bus is pulled up at point “b”, the slave device reads data on the SDA line,

that is data in master 2.

Data transmitted from master 1 becomes invalid. The state in master 1 is called

“arbitration lost”. A master device which loses arbitration releases the SDA pin and

the SCL pin in order not to effect data transmitted from other masters with arbitration.

When more than one master sends the same data at the first word, arbitration occurs

continuously after the second word.

Figure 2.9.11 Arbitration Lost

SDA (Bus)

SDA pin becomes “1” after losing arbitration.

SCL (Bus)

SDA pin (Master 2)

SDA pin (Master 1)

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