HT45F23 datasheet(88/152 Pages) HOLTEK

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2C Interface

The I

2C 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.

2C Interface Operation

The I

2C 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

2C bus is identified by a unique address which will be

transmitted and received on the I

2C bus.

When two devices communicate with each other on the bidirectional I

2C 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

2C bus, the slave transmit

mode and the slave receive mode.

There are several configuration options associated with the I

2C 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 exists to allow a clock other than the system clock to drive the I

2C interface.

Another configuration option determines the debounce time of the I

2C interface. This uses the internal

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 1 or

2 system clocks.

2C Registers

There are three control registers associated with the I

2C bus, SIMC0,

SIMC1 and SIMA and one data register, SIMD. The SIMD register,

which is shown in the above SPI section, is used to store the data being

transmitted and received on the I

2C bus. Before the microcontroller

writes data to the I

2C bus, the actual data to be transmitted must be placed

in the SIMD register. After the data is received from the I

2C bus, the

microcontroller can read it from the SIMD register. Any transmission or

reception of data from the I

2C bus must be made via the SIMD register.

Note that the SIMA register also has the name SIMC2 which is used by the

SPI function. Bit SIMEN and bits SIM2~SIM0 in register SIMC0 are used

by the I

2C interface.

Rev. 1.20

September 15, 2011

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

D e v i c e

S l a v e

D e v i c e

M a s t e r

D e v i c e

S l a v e

V D D

S D A

S C L

2C Master Slave Bus Connection

S T A R T s i g n a l

f r o m M a s t e r

S e n d s l a v e a d d r e s s

a n d R / W b i t f r o m M a s t e r

A c k n o w l e d g e

f r o m s l a v e

S e n d d a t a b y t e

f r o m M a s t e r

A c k n o w l e d g e

f r o m s l a v e

S T O P s i g n a l

f r o m M a s t e r

HT45F23 Datasheet(PDF) 88 Page - Holtek Semiconductor Inc

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