HT45R37 datasheet(46/100 Pages) HOLTEK

46 / 100 page

HT45R37

Rev. 1.10

January 29, 2010

· SRW

The SRW bit is the Slave Read/Write bit. This bit de-

termines whether the master device wishes to trans-

mit or receive data from the I

2C bus. When the

transmitted address and slave address match, that is

when the HAAS bit is set high, the device will check

the SRW bit to determine whether it should be in

transmit mode or receive mode. If the SRW bit is high,

the master is requesting to read data from the bus, so

the device should be in transmit mode. When the

SRW bit is zero, the master will write data to the bus,

therefore the device should be in receive mode to

read this data.

· TXAK

The TXAK flag is the transmit acknowledge flag. After

the receipt of 8-bits of data, this bit will be transmitted

to the bus on the 9th clock. To continue receiving more

data, this bit has to be reset to zero before further data

is received.

· HTX

The HTX flag is the transmit/receive mode bit. This

flag should be set high to set the transmit mode and

low for the receive mode.

· HBB

The HBB flag is the I

2C busy flag. This flag will be high

when the I

2C bus is busy which will occur when a

START signal is detected. The flag will be reset to

zero when the bus is free which will occur when a

STOP signal is detected.

· HASS

The HASS flag is the address match flag. This flag is

used to determine if the slave device address is the

same as the master transmit address. If the ad-

dresses match then this bit will be high, if there is no

match then the flag will be low.

· HCF

The HCF flag is the data transfer flag. This flag will be

zero when data is being transferred. Upon completion

of an 8-bit data transfer the flag will go high and an in-

terrupt will be generated.

2C Control Register - SIMAR

The SIMARregister is also used by the SPI interface but

has the name SIMCTL2.

The SIMAR register is the location where the 7-bit slave

address of the microcontroller is stored. Bits 1~7 of the

SIMAR register define the microcontroller slave ad-

dress. Bit 0 is not defined. When a master device, which

is connected to the I

2C bus, sends out an address,

which matches the slave address in the SIMARregister,

the microcontroller slave device will be selected. Note

that the SIMAR register is the same register as

SIMCTL2 which is used by the SPI interface.

2C Bus Communication

Communication on the I

2C bus requires four separate

steps, a START signal, a slave device address transmis-

sion, a data transmission and finally a STOP signal.

When a START signal is placed on the I

2C bus, all de-

vices 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 microcontroller

matches that of the transmitted address, the HAAS bit in

the SIMCTL1 register will be set and an I

2C interrupt will

be generated. After entering the interrupt service rou-

tine, the microcontroller slave device must first check

the condition of the HAAS bit to determine whether the

interrupt source originates from an address match or

from the completion of an 8-bit data transfer. 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 whose value will be placed in the SRW

bit. This bit will be checked by the microcontroller to de-

termine whether to go into transmit or receive mode. Be-

fore any transfer of data to or from the I

2C bus, the

microcontroller must initialise the bus, the following are

steps to achieve this:

Step 1

Write the slave address of the microcontroller to the I

bus address register SIMAR.

S I M A R R e g i s t e r

b 7

U n d e f i n e d

I 2 C d e v i c e s l a v e a d d r e s s

b 0

S A 5

S A 4

S A 6

S A 0

S A 3

S A 2

S A 1

2C Slave Address Register

- SIMAR

S t a r t

W r i t e S l a v e

A d d r e s s t o S I M A R

S E T S I M [ 2 : 0 ] = 1 1 0

S E T S I M E N

I 2 C B u s

I n t e r r u p t = ?

E n a b l e

D i s a b l e

S E T E S I M

S e t E M F I 0

W a i t f o r I n t e r r u p t

G o t o M a i n P r o g r a m

C L R E S I M

P o l l S I M F t o d e c i d e

w h e n t o g o t o I 2 C B u s I S R

G o t o M a i n P r o g r a m

2C Bus Initialisation Flow Chart

HT45R37 Datasheet(PDF) 46 Page - Holtek Semiconductor Inc

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