DSPIC30F2010 datasheet(97/202 Pages) MICROCHIP

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DS70118J-page 97

dsPIC30F2010

16.2

I2C Module Addresses

The I2CADD register contains the Slave mode

addresses. The register is a 10-bit register.

If the A10M bit (I2CCON<10>) is ‘0’, the address is

interpreted by the module as a 7-bit address. When an

address is received, it is compared to the 7 LSbs of the

I2CADD register.

If the A10M bit is ‘1’, the address is assumed to be a

10-bit address. When an address is received, it will be

compared with the binary value ‘1 1 1 1 0 A9 A8’

(where A9, A8 are two Most Significant bits of

I2CADD). If that value matches, the next address will

be compared with the Least Significant 8 bits of

I2CADD, as specified in the 10-bit addressing protocol.

TABLE 16-1:

7-BIT I

2C™ SLAVE

ADDRESSES SUPPORTED BY

dsPIC30F

16.3

I2C 7-bit Slave Mode Operation

Once enabled (I2CEN = 1), the slave module will wait

for a Start bit to occur (i.e., the I2C module is ‘Idle’).

Following the detection of a Start bit, 8 bits are shifted

into I2CRSR and the address is compared against

I2CADD. In 7-bit mode (A10M = 0), bits I2CADD<6:0>

are compared against I2CRSR<7:1> and I2CRSR<0>

is the R_W bit. All incoming bits are sampled on the

rising edge of SCL.

If an address match occurs, an acknowledgement will

be sent, and the slave event interrupt flag (SI2CIF) is

set on the falling edge of the ninth (ACK) bit. The

address match does not affect the contents of the

I2CRCV buffer or the RBF bit.

16.3.1

SLAVE TRANSMISSION

If the R_W bit received is a ‘1’, then the serial port will

go into Transmit mode. It will send ACK on the ninth bit

and then hold SCL to ‘0’ until the CPU responds by writ-

ing to I2CTRN. SCL is released by setting the SCLREL

bit, and 8 bits of data are shifted out. Data bits are

shifted out on the falling edge of SCL, such that SDA is

valid during SCL high (see timing diagram). The inter-

rupt pulse is sent on the falling edge of the ninth clock

pulse, regardless of the status of the ACK received

from the master.

16.3.2

SLAVE RECEPTION

If the R_W bit received is a ‘0’ during an address

match, then Receive mode is initiated. Incoming bits

are sampled on the rising edge of SCL. After 8 bits are

received, if I2CRCV is not full or I2COV is not set,

I2CRSR is transferred to I2CRCV. ACK is sent on the

ninth clock.

If the RBF flag is set, indicating that I2CRCV is still

holding data from a previous operation (RBF = 1), then

ACK is not sent; however, the interrupt pulse is gener-

ated. In the case of an overflow, the contents of the

I2CRSR are not loaded into the I2CRCV.

16.4

I2C 10-bit Slave Mode Operation

In 10-bit mode, the basic receive and transmit opera-

tions are the same as in the 7-bit mode. However, the

criteria for address match is more complex.

The I2C specification dictates that a slave must be

addressed for a write operation, with two address bytes

following a Start bit.

The A10M bit is a control bit that signifies that the

address in I2CADD is a 10-bit address rather than a

7-bit address. The address detection protocol for the

first byte of a message address is identical for 7-bit

and 10-bit messages, but the bits being compared are

different.

I2CADD holds the entire 10-bit address. Upon receiv-

ing an address following a Start bit, I2CRSR <7:3> is

compared against a literal ‘11110’ (the default 10-bit

address) and I2CRSR<2:1> are compared against

I2CADD<9:8>. If a match occurs and if R_W = 0, the

interrupt pulse is sent. The ADD10 bit will be cleared to

indicate a partial address match. If a match fails or

R_W = 1, the ADD10 bit is cleared and the module

returns to the Idle state.

The low byte of the address is then received and com-

pared with I2CADD<7:0>. If an address match occurs,

the interrupt pulse is generated and the ADD10 bit is

set, indicating a complete 10-bit address match. If an

address match did not occur, the ADD10 bit is cleared

and the module returns to the Idle state.

16.4.1

10-BIT MODE SLAVE

TRANSMISSION

Once a slave is addressed in this fashion, with the full 10-

bit

address

(we

will

refer

this

state

“PRIOR_ADDR_MATCH”), the master can begin sending

data bytes for a slave reception operation.

Address

Range

Description Address

0x00

General call address or Start byte

0x01-0x03

Reserved

0x04-0x07

Hs mode master codes

0x08-0x77

Valid 7-bit addresses

0x78-0x7B

Valid 10-bit addresses (lower 7 bits)

0x7C-0x7F

Reserved

Note:

The I2CRCV will be loaded if the I2COV

bit = 1 and the RBF flag = 0. In this case,

a read of the I2CRCV was performed, but

the user did not clear the state of the

I2COV

bit

before

the

receive

occurred. The acknowledgement is not

sent (ACK = 1) and the I2CRCV is

updated.

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