TMP92CZ26A

92CZ26A-354

(8) Interrupt service requests and interrupt cancellation
When a serial bus interface interrupt request (INTSBI) occurs, the SBICR2 <PIN>
is cleared to “0”. During the time that the SBI CR2< P IN> is “0”, the SCL lin e is pulled
down to the Low level.
The <PIN> is cleared to “0” when a 1-word of data is transmitted or received. Either
writing/reading data to/fr om SBID BR sets the <PIN> to “1”.
The time from the <PIN> being set to “1” until the SCL lin e is released takes tLOW.
In the address recognition mode (<ALS> = “0”), <PIN> is cleared to “0” when the
received slave address is the same as the value set at the I2CAR or when a GENERAL
CALL is received (all 8-bit data are “0” after a start condition). Although
SBICR2<PIN> can be set to “1” by t he program, the <PIN> is not clear it to “0” when it
is written “0”.
(9) Serial bus interface operation mode selection
SBICR2<SBIM1:0> is used to specify the serial bus interface operation mode. Set
SBICR2< SBIM1:0> to “10” when the device is to be used in I2C Bus Mode after
confirming pin condit io n of serial bus interface to “H”.
Switch a mode to port after confirming a bus is free.
(10) Arbitration lost detect ion monitor
Since more than one master device can exist simultaneously on the bus in I2C Bus
Mode, a bus arbitration procedure has been implemented in order to guarantee the
integrity of transf erred data.
In case set start condition bit with bus is busy, start condition is not output on SCL
and SDA pin, but arbitrat ion lost is generated.
Data on the SDA line is used for I2C bus arbitration.
The following shows an example of a bus arbitration procedure when two master
devices exist sim ultaneously on th e bus. Master A and Master B output the same data
until point “a”. After Master A outputs “L” and Mast er B, “H”, the SDA lin e of the bus
is wire-AND and th e SDA lin e is pulled do wn to the Low- level by Master A. When th e
SCL line of the bus is pulled up at point b, the slave device reads the data on the SDA
line, that is, data in Master A. A data transmitted from Master B becomes invalid. The
state in Master B is called “ARBITRATION LOST”. Master B device which loses
arbitration releases the internal SDA output in order not to affect data transmitted
from other masters with arbitra tion. When more than one master sends the same data
at the first word, arbitration occurs continuously after the second word.
Figure 3.15.12 Arbitration lost
The TMP92C Z26A compares the levels on the bus’s SDA lin e with those of the internal
SDA output on the risin g edge of the SCL line. If th e levels do not match, arbi tration is
Internal SDA output becomes 1 after arbitration has been lost.
SCL pin
Internal SDA output
(Master A)
Internal SDA output
(Master B)
SDA pin
ab