Toshiba H1 Series - Manual (Page 357)

TMP92CZ26A
92CZ26A-354
(8) Interrupt service requests and interrupt cancellation
When a serial bus interface interrupt request (INTSBI) occurs, the SBICR2
is cleared to “0”. During the time that the SBICR2 is “0”, the SCL line is pulled
down to the Low level.
The is cleared to “0” when a 1-word of data is transmitted or received. Either
writing/reading data to/from SBIDBR sets the to “1”.
The time from the being set to “1” until the SCL line is released takes t
LOW
.
In the address recognition mode ( = “0”), 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 can be set to “1” by the program, the is not clear it to “0” when it
is written “0”.
(9) Serial bus interface operation mode selection
SBICR2 is used to specify the serial bus interface operation mode. Set
SBICR2< SBIM1:0> to “10” when the device is to be used in I 2 C Bus Mode after
confirming pin condition of serial bus interface to “H”.
Switch a mode to port after confirming a bus is free.
(10) Arbitration lost detection monitor
Since more than one master device can exist simultaneously on the bus in I 2 C Bus
Mode, a bus arbitration procedure has been implemented in order to guarantee the
integrity of transferred data.
In case set start condition bit with bus is busy, start condition is not output on SCL
and SDA pin, but arbitration lost is generated.
Data on the SDA line is used for I
2 C bus arbitration.
The following shows an example of a bus arbitration procedure when two master
devices exist simultaneously on the bus. Master A and Master B output the same data
until point “a”. After Master A outputs “L” and Master B, “H”, the SDA line of the bus
is wire-AND and the SDA line is pulled down to the Low-level by Master A. When the
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 arbitration. 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 TMP92CZ26A compares the levels on the bus’s SDA line with those of the internal
SDA output on the rising edge of the SCL line. If the levels do not match, arbitration 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
a b