
Philips Semiconductors
I2C Interface
PRODUCT SPECIFICATION
16-5
served by software, and the hardware I
2
C interface is
disconnected from the SCL and SDA pins. Refer to
Figure 16-3
for a clarification of the principles involved.
Software mode is by default disabled after boot. Soft-
ware
mode
is
enabled
IIC_CR.SW_MODE_EN. At that point, the SCL and SDA
pins can be controlled by the IIC_CR SDA_OUT and
SCL_OUT bits. Writing a ‘1’ to either bit causes the cor-
responding pin to become active, i.e. be pulled low. The
SDA and SCL lines are open-collector outputs, and can
hence also be pulled low by external devices. The actual
pin state can be observed by software by examining
IIC_SR SDA_STAT and SCL_STAT bits. A 1 in these
MMIO bits indicates that the corresponding pin is cur-
rently pulled low.
By appropriate software, possibly using a timer interrupt,
full I
2
C functionality can be implemented using this
mechanism.
by
writing
a
‘1’
to
16.6
I
2
C HARDWARE OPERATION MODE
Hardware operation of I
2
C is the default mode after boot.
The TM1300 I
2
C hardware interface operates in one of
two modes:
1. Master-transmitter (to write data to a slave)
2. Master-receiver (to read data from a slave)
As a master, the I
2
C logic will generate all the serial clock
pulses and the START and STOP bus conditions. The
START and STOP bus conditions are shown in
Figure 16-4
. A transfer is ended with a STOP condition
or a repeated START condition. Since a repeated
START condition is also the beginning of the next serial
transfer, the I
2
C bus will not be released.
Note:
The I
2
C interface on TM1300 will operate as a
master ONLY!
The number of bytes transferred between the START
and STOP conditions from transmitter to receiver is not
limited. Each 8-bit data byte is followed by one acknowl-
edge bit. The transmitter releases the SDA line which will
pull-up to a HIGH level during the acknowledge bit time.
The receiver acknowledges by pulling the data line LOW
SCL
SDA
hardware
DATA
HIWAY
open drain
scl_stat
scl_out
I2C
D Q
sda_stat
sda_out
tribuf
tribuf
sw_mode_en
sw_mode_en
buf
open drain
buf
D Q
Figure 16-3. I
2
C
software mode only logic
SDA
SCL
S
P
START
STOP
Figure 16-4. START and STOP Conditions on I
2
C