PIC16F87 datasheet(95/230 Pages) MICROCHIP

95 / 230 page

 2002-2013 Microchip Technology Inc.

DS30487D-page 95

PIC16F87/88

10.3.2

MASTER MODE OPERATION

Master mode operation is supported in firmware using

interrupt generation on the detection of the Start and

Stop conditions. The Stop (P) and Start (S) bits are

cleared from a Reset, or when the SSP module is dis-

abled. The Stop (P) and Start (S) bits will toggle based

on the Start and Stop conditions. Control of the I2C bus

may be taken when the P bit is set, or the bus is Idle

and both the S and P bits are clear.

In Master mode operation, the SCL and SDA lines are

manipulated in firmware by clearing the corresponding

TRISB<4,1> bit(s). The output level is always low, irre-

spective of the value(s) in PORTB<4,1>. So, when

transmitting data, a ‘1’ data bit must have the

TRISB<1> bit set (input) and a ‘0’ data bit must have

the TRISB<1> bit cleared (output). The same scenario

is true for the SCL line with the TRISB<4> bit. Pull-up

resistors must be provided externally to the SCL and

SDA pins for proper operation of the I2C module.

The following events will cause the SSP Interrupt Flag

bit, SSPIF, to be set (SSP Interrupt if enabled):

• Start condition

• Stop condition

• Data transfer byte transmitted/received

Master mode operation can be done with either the

Slave mode Idle (SSPM3:SSPM0 = 1011), or with the

Slave mode active. When both Master mode operation

and Slave modes are used, the software needs to

differentiate the source(s) of the interrupt.

For more information on Master mode operation, see

Application Note AN554, “Software Implementation of

I2C™ Bus Master”.

10.3.3

MULTI-MASTER MODE OPERATION

In Multi-Master mode operation, the interrupt genera-

tion on the detection of the Start and Stop conditions

allows the determination of when the bus is free. The

Stop (P) and Start (S) bits are cleared from a Reset, or

when the SSP module is disabled. The Stop (P) and

Start (S) bits will toggle based on the Start and Stop

conditions. Control of the I2C bus may be taken when

bit P (SSPSTAT<4>) is set, or the bus is Idle and both

the S and P bits clear. When the bus is busy, enabling

the SSP interrupt will generate the interrupt when the

Stop condition occurs.

In Multi-Master mode operation, the SDA line must be

monitored to see if the signal level is the expected out-

put level. This check only needs to be done when a

high level is output. If a high level is expected and a low

level is present, the device needs to release the SDA

and SCL lines (set TRISB<4,1>). There are two stages

where this arbitration can be lost:

• Address Transfer

• Data Transfer

When the slave logic is enabled, the slave device

continues to receive. If arbitration was lost during the

address transfer stage, communication to the device

may be in progress. If addressed, an ACK pulse will be

generated. If arbitration was lost during the data

transfer stage, the device will need to retransfer the

data at a later time.

For more information on Multi-Master mode operation,

see Application Note AN578, “Use of the SSP Module

in the of I2C™ Multi-Master Environment”.

TABLE 10-3:

REGISTERS ASSOCIATED WITH I2C™ OPERATION

Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value on

POR, BOR

Value on

all other

Resets

0Bh, 8Bh,

10Bh,18Bh

INTCON

GIE

PEIE

TMR0IE

INT0IE

RBIE

TMR0IF INT0IF

RBIF

0000 000x

0000 000u

0Ch

PIR1

—

ADIF(1)

RCIF

TXIF

SSPIF CCP1IF TMR2IF TMR1IF

-000 0000

8Ch

PIE1

—

ADIE(1)

RCIE

TXIE

SSPIE CCP1IE TMR2IE TMR1IE

-000 0000

13h

SSPBUF

Synchronous Serial Port Receive Buffer/Transmit Register

xxxx xxxx

uuuu uuuu

93h

SSPADD

Synchronous Serial Port (I2C mode) Address Register

0000 0000

14h

SSPCON

WCOL

SSPOV

SSPEN

CKP

SSPM3 SSPM2 SSPM1 SSPM0

0000 0000

94h

SSPSTAT

SMP(2)

CKE(2)

D/A

R/W

0000 0000

86h

TRISB

PORTB Data Direction Register

1111 1111

Legend:

= unknown, u = unchanged, - = unimplemented locations read as ‘0’.

Shaded cells are not used by SSP module in SPI mode.

Note

This bit is only implemented on the PIC16F88. The bit will read ‘0’ on the PIC16F87.

Maintain these bits clear in I2C™ mode.

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