
Philips Semiconductors
I2C Interface
PRODUCT SPECIFICATION
16-5
served by software, and the hardware I2C 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
by
writing
a
‘1’
to
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.A1in these
MMIO bits indicates that the corresponding pin is cur-
rently pulled low.
By appropriate software, possibly using a timer interrupt,
full I2C functionality can be implemented using this
mechanism.
16.6
I2C HARDWARE OPERATION MODE
Hardware operation of I2C is the default mode after boot.
The TM1300 I2C 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 I2C 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 I2C bus will not be released.
Note:
The I2C 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
DQ
sda_stat
sda_out
tribuf
sw_mode_en
buf
open drain
buf
DQ
Figure 16-3. I2C software mode only logic
SDA
SCL
S
P
START
STOP
Figure 16-4. START and STOP Conditions on I2C