HT85F2270 datasheet(182/226 Pages) HOLTEK

182 / 226 page

Rev. 1.00

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

I2C Bus Communication

Communication on the I2C bus requires four separate steps, a START signal, a slave device address

transmission, a data transmission and finally a STOP signal. When a START signal is placed on

the I2C bus, all devices on the bus will receive this signal and be notified of the imminent arrival of

data on the bus. The first seven bits of the data will be the slave address with the first bit being the

MSB. If the address of the slave device matches that of the transmitted address, which means one

of the I2C states is matched, the SI bit in the I2CCON register will be set and an I2C interrupt will

be generated. After entering the interrupt service routine, the devices must first check the status

of the I2CSTA register to determine the interrupt source originating condition. The SI bit is set by

hardware when one of 25 out of 26 possible I2C states is entered. The only state that does not set

the SI bit is the state F8H, which indicates that no relevant state information is available The SI bit

must be cleared by the application program.

During a data transfer, note that after the 7-bit slave address has been transmitted, the following bit,

which is the 8th bit, is the read/write bit. This bit will be checked by the slave device to determine

whether to go into transmit or receive mode. Before any transfer of data to or from the I2C bus, the

microcontroller must initialise the bus. The following are the steps to achieve this:

■

Step 1

Set the ENS1 bit in the I2CCON register high to enable the I2C bus.

■

Step 2

Write the slave address of the device to the I2C bus address register I2CADR.

■

Step 3

Set the EI2C interrupt enable bit of the interrupt control register to enable the I2C interrupt.

St ar t

Wr it e Sl av e

Ad dr es s to I 2C AD R

SE T EN S1

I 2 C Bu s

In te rr upt =?

Ye s

SE T SI

Wa it fo r In te rr up t

G ot o Ma in P r ogr am

CL R EI 2C

Po ll S I to d ec id e

wh en to e xe cu te I SR

G ot o Ma in P r ogr am

I2C Bus Initialisation Flow Chart

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