PIC16F818-ESLASHML datasheet(78/176 Pages) MICROCHIP

78 / 176 page

PIC16F818/819

DS39598E-page 76

 2004 Microchip Technology Inc.

10.3

SSP I2C Mode 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 functions. 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

RB4/SCK/SCL pin, which is the clock (SCL) and the

RB1/SDI/SDA pin, which is the data (SDA). The user

must configure these pins as inputs or outputs through

the TRISB<4,1> bits.

To ensure proper communication of the I2C Slave mode,

the TRIS bits (TRISx [SDA, SCL]) corresponding to the

I2C pins must be set to ‘1’. If any TRIS bits (TRISx<7:0>)

of the port containing the I2C pins (PORTx [SDA, SCL])

are changed in software during I2C communication

using a Read-Modify-Write instruction (BSF, BCF), then

the I2C mode may stop functioning properly and I2C

communication may suspend. Do not change any of the

TRISx bits (TRIS bits of the port containing the I2C pins)

using the instruction BSF or BCF during I2C communica-

tion. If it is absolutely necessary to change the TRISx

bits during communication, the following method can be

used:

EXAMPLE 10-1:

The SSP module functions are enabled by setting SSP

Enable bit, SSPEN (SSPCON<5>).

FIGURE 10-5:

SSP BLOCK DIAGRAM

(I2C™ MODE)

The SSP module has five registers for I2C operation:

• 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 to support Firmware

Master mode

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

Stop bit interrupts enabled to support Firmware

Master mode

•I2C Firmware Controlled Master mode with Start

and Stop bit interrupts enabled, slave is Idle

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

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

provided these pins are programmed to inputs by

setting the appropriate TRISB bits. Pull-up resistors

must be provided externally to the SCL and SDA pins

for proper operation of the I2C module.

Additional information on SSP I2C operation may be

found in the “PICmicro® Mid-Range MCU Family

Reference Manual” (DS33023).

MOVF

TRISC, W

; Example for an 18-pin part such as the PIC16F818/819

IORLW

0x18

; Ensures <4:3> bits are ‘11’

ANDLW

B’11111001’

; Sets <2:1> as output, but will not alter other bits

; User can use their own logic here, such as IORLW, XORLW and ANDLW

MOVWF

TRISC

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)

RB4/SCK/

RB1/

Shift

Clock

MSb

SDI/

LSb

SDA

SCL

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