Philips CEM2100/00, Service Manual

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Page 203
T
5CL8
In the slave mode, the conditions of generating INTSBI interrupt request are follows:
• At the end of acknowledge signal when the received slave address matches to the value set by the
I2CAR
• At the end of acknowledge signal when a “GENERAL CALL” is received
• At the end of transferring or receiving after matching of slave address or receiving of “GENERAL
CALL”
When a serial bus interface interrupt request occurs, the PIN (Bit4 in SBISRB) is cleared to “0”. During the
time that the PIN is “0”, the SCL pin is pulled-down to low level.
Either writing data to SBIDBR or reading data from the SBIDBR sets the PIN to “1”.
The time from the PIN being set to “1” until the SCL pin is released takes t
LOW
.
Although the PIN (Bit4 in SBICRB) can be set to “1” by the softrware, the PIN can not be cleared to “0” by
the softrware.
Note:When the arbitration lost occurs, if the slave address sent from the other master devices is not match, the
INTSBI interrupt request is generated. But the PIN is not cleared.
16.5.9 Setting of I
2
C bus mode
The SBIM (Bit3 and 2 in SBICRB) is used to set I
2
C bus mode.
Set the SBIM to “10” in order to set I
2
C bus mode. Before setting of I
2
C bus mode, confirm serial bus inter-
face pins in a high level, and then, write “10” to SBIM. And switch a port mode after confirming that a bus is
free.
16.5.10Arbitration lost detection monitor
Since more than one master device can exist simultaneously on a bus, a bus arbitration procedure is imple-
mented in order to guarantee the contents of transferred data.
Data on the SDA line is used for bus arbitration of the I
2
C bus.
The following shows an example of a bus arbitration procedure when two master devices exist simulta-
neously on a bus. Master 1 and Master 2 output the same data until point “a”. After that, when Master 1 outputs
“1” and Master 2 outputs “0”, since the SDA line of a bus is wired 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 16-7 Arbitration Lost
The serial bus interface circuit compares levels of a SDA line of a bus with its SDA pin at the rising edge of
the SCL line. If the levels are unmatched, arbitration is lost and the AL (Bit3 in SBISRB) is set to “1”.
a b
SCL (Bus)
SDA pin (Master 1)
SDA pin (Master 2)
SDA (Bus)
SDA pin becomes "1" after losing arbitration.