Rev. 2.10
176
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Rev. 2.10
177
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HT68F20/HT68F30/HT68F40/HT68F50/HT68F60
HT68FU30/HT68FU40/HT68FU50/HT68FU60
Enhanced I/O Flash Type 8-Bit MCU with EEPROM
HT68F20/HT68F30/HT68F40/HT68F50/HT68F60
HT68FU30/HT68FU40/HT68FU50/HT68FU60
Enhanced I/O Flash Type 8-Bit MCU with EEPROM
I
2
C Interface
The I
2
C interface is used to communicate with external peripheral devices such as sensors,
EEPROM memory etc. Originally developed by Philips, it is a two line low speed serial interface
for synchronous serial data transfer. The advantage of only two lines for communication, relatively
simple communication protocol and the ability to accommodate multiple devices on the same bus
has made it an extremely popular interface type for many applications.
I
2
C Master Slave Bus Connection
I
2
C Interface Operation
The I
2
C serial interface is a two line interface, a serial data line, SDA, and serial clock line, SCL. As
many devices may be connected together on the same bus, their outputs are both open drain types.
For this reason it is necessary that external pull-high resistors are connected to these outputs. Note
that no chip select line exists, as each device on the I
2
C bus is identified by a unique address which
will be transmitted and received on the I
2
C bus.
When two devices communicate with each other on the bidirectional I
2
C bus, one is known as the
master device and one as the slave device. Both master and slave can transmit and receive data,
however, it is the master device that has overall control of the bus. For these devices, which only
operates in slave mode, there are two methods of transferring data on the I
2
C bus, the slave transmit
mode and the slave receive mode.
There are several configuration options associated with the I
2
C interface. One of these is to enable
the function which selects the SIM pins rather than normal I/O pins. Note that if the configuration
option does not select the SIM function then the SIMEN bit in the SIMC0 register will have no
effect. A configuration option determines the debounce time of the I
2
C interface. This uses the
system clock to in effect add a debounce time to the external clock to reduce the possibility of
glitches on the clock line causing erroneous operation. The debounce time, if selected, can be
chosen to be either 2 or 4 system clocks. To achieve the required I
2
C data transfer speed, there
exists a relationship between the system clock, f
SYS
, and the I
2
C debounce time. For either the I
2
C
Standard or Fast mode operation, users must take care of the selected system clock frequency and
the configured debounce time to match the criterion shown in the following table.
I
2
C Debounce Time Selection
I
2
C Standard Mode (100kHz)
I
2
C Fast Mode (400kHz)
No debo�nce
f
SYS
>2MHz
f
SYS
>5MHz
2 s�stem c�ock debo�nce
f
SYS
>�MHz
f
SYS
>10MHz
� s�stem c�ock debo�nce
f
SYS
>8MHz
f
SYS
>20MHz
I
2
C Minimum f
SYS
Frequency