PIC16C925-SSLASHCL datasheet(71/182 Pages) MICROCHIP

71 / 182 page

 2001 Microchip Technology Inc.

Preliminary

DS39544A-page 69

PIC16C925/926

9.3

SSP I2C Operation

The SSP module in I2C mode fully implements all slave

functions, except general call support, and provides

interrupts on START and STOP bits in hardware to

facilitate firmware implementations of the master func-

tions. The SSP module implements the standard mode

specifications as well as 7-bit and 10-bit addressing.

Two pins are used for data transfer. These are the

RC3/SCK/SCL pin, which is the clock (SCL), and the

RC4/SDI/SDA pin, which is the data (SDA). The user

must configure these pins as inputs or outputs through

the TRISC<4:3> bits. The SSP module functions are

enabled

setting

SSP

enable

bit,

SSPEN

(SSPCON<5>).

FIGURE 9-16:

SSP BLOCK DIAGRAM

(I2C MODE)

The SSP module has five registers for I2C operation.

These are the:

• SSP Control Register (SSPCON)

• SSP Status Register (SSPSTAT)

• Serial Receive/Transmit Buffer (SSPBUF)

• SSP Shift Register (SSPSR) - Not directly

accessible

• SSP Address Register (SSPADD)

The SSPCON register allows control of the I2C opera-

tion. Four mode selection bits (SSPCON<3:0>) allow

one of the following I2C modes to be selected:

• I2C Slave mode (7-bit address)

• I2C Slave mode (10-bit address)

• I2C Slave mode (7-bit address), with START and

STOP bit interrupts enabled

• I2C Slave mode (10-bit address), with START and

STOP bit interrupts enabled

• I2C Firmware controlled Master mode, slave is

idle

Selection of any I2C mode, with the SSPEN bit set,

forces the SCL and SDA pins to be open drain, pro-

vided these pins are programmed to inputs by setting

the appropriate TRISC bits.

The SSPSTAT register gives the status of the data

transfer. This information includes detection of a

START or STOP bit, specifies if the received byte was

data or address, if the next byte is the completion of

10-bit address, and if this will be a read or write data

transfer. The SSPSTAT register is read only.

The SSPBUF is the register to which transfer data is

written to or read from. The SSPSR register shifts the

data in or out of the device. In receive operations, the

SSPBUF and SSPSR create a doubled buffered

receiver. This allows reception of the next byte to begin

before reading the last byte of received data. When the

complete byte is received, it is transferred to the

SSPBUF register and flag bit SSPIF is set. If another

complete byte is received before the SSPBUF register

is read, a receiver overflow has occurred and bit

SSPOV (SSPCON<6>) is set and the byte in the

SSPSR is lost.

The SSPADD register holds the slave address. In

10-bit mode, the user needs to write the high byte of the

address (1111 0 A9 A8 0). Following the high byte

address match, the low byte of the address needs to be

loaded (A7:A0).

Read

Write

SSPSR reg

Match Detect

SSPADD reg

START and

STOP bit Detect

SSPBUF reg

Internal

Data Bus

Addr Match

Set, Reset

S, P bits

(SSPSTAT reg)

RC3/SCK/SCL

RC4/

Shift

Clock

MSb

SDI/

LSb

SDA

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