PIC16F87X datasheet(73/218 Pages) MICROCHIP

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DS30292D-page 73

PIC16F87X

9.2

MSSP I2C Operation

The MSSP module in I2C mode, fully implements all

master and slave functions (including general call sup-

port) and provides interrupts on START and STOP bits in

hardware, to determine a free bus (multi-master func-

tion). The MSSP module implements the standard mode

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

Refer to Application Note AN578, "Use of the SSP

Module in the I 2C Multi-Master Environment."

A "glitch" filter is on the SCL and SDA pins when the pin

is an input. This filter operates in both the 100 kHz and

400 kHz modes. In the 100 kHz mode, when these pins

are an output, there is a slew rate control of the pin that

is independent of device frequency.

FIGURE 9-5:

I2C SLAVE MODE BLOCK

DIAGRAM

Two pins are used for data transfer. These are the SCL

pin, which is the clock, and the SDA pin, which is the

data. The SDA and SCL pins are automatically config-

ured when the I2C mode is enabled. The SSP module

functions are enabled by setting SSP Enable bit

SSPEN (SSPCON<5>).

The MSSP module has six registers for I2C operation.

They are the:

• SSP Control Register (SSPCON)

• SSP Control Register2 (SSPCON2)

• 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 Master mode, clock = OSC/4 (SSPADD +1)

•I2C firmware modes (provided for compatibility to

other mid-range products)

Before selecting any I2C mode, the SCL and SDA pins

must be programmed to inputs by setting the appropri-

ate TRIS bits. Selecting an I2C mode by setting the

SSPEN bit, enables the SCL and SDA pins to be used

as the clock and data lines in I2C mode. Pull-up resis-

tors must be provided externally to the SCL and SDA

pins for the proper operation of the I2C module.

The CKE bit (SSPSTAT<6:7>) sets the levels of the

SDA and SCL pins in either Master or Slave mode.

When CKE = 1, the levels will conform to the SMBus

specification. When CKE = 0, the levels will conform to

the I2C specification.

The SSPSTAT register gives the status of the data

transfer. This information includes detection of a

START (S) or STOP (P) bit, specifies if the received

byte was data or address, if the next byte is the com-

pletion of 10-bit address, and if this will be a read or

write data transfer.

SSPBUF is the register to which the 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)

SCL

Shift

Clock

MSb

LSb

SDA

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