PIC17C752-08SLASHP datasheet(139/320 Pages) MICROCHIP

139 / 320 page

Preliminary

DS30264A-page 139

PIC17C75X

An SSP interrupt is generated for each data transfer

byte. Flag bit SSPIF must be cleared in software, and

the SSPSTAT register is used to determine the status

of the byte. Flag bit SSPIF is set on the falling edge of

the ninth clock pulse.

As a slave-transmitter, the ACK pulse from the mas-

ter-receiver is latched on the rising edge of the ninth

SCL input pulse. If the SDA line was high (not ACK),

then the data transfer is complete. When the ACK is

latched by the slave, the slave logic is reset and the

slave then monitors for another occurrence of the

START bit. If the SDA line was low (ACK), the transmit

data must be loaded into the SSPBUF register, which

also loads the SSPSR register. Then the SCL pin

should be enabled by setting bit CKP.

15.2.2

GENERAL CALL ADDRESS SUPPORT

The addressing procedure for the I2C bus is such that

the ﬁrst byte after the START condition usually deter-

mines which device will be the slave addressed by the

master.

The exception is the general call address

which can address all devices. When this address is

used, all devices should, in theory, respond with an

acknowledge.

The general call address is one of eight addresses

reserved for speciﬁc purposes by the I2C protocol. It

consists of all 0’s with R/W = 0

The general call address is recognized when the Gen-

eral Call Enable bit (GCEN) is enabled (SSPCON2<7>

= 1). Following a start-bit detect, 8-bits are shifted into

SSPSR

and

the

address

compared

against

SSPADD, and is also compared to the general call

address, ﬁxed in hardware.

If the general call address matches, the SSPSR is

transfered to the SSPBUF, the BF ﬂag is set (eigth bit),

and on the falling edge of the ninth bit (ACK bit) the

SSPIF interrupt is set.

When the interrupt is serviced. The source for the

interrupt can be checked by reading the contents of

the SSPBUF to determine if the address was device

speciﬁc or a general call address.

In 10-bit mode, the SSPADD is required to be updated

for the second half of the address to match, and the

UA bit is set (SSPSTAT<1>).

If the general call

address is sampled when GCEN = 1 while the slave is

conﬁgured in 10-bit address mode, then the second

half of the address is not necessary, the UA bit will not

be set, and the slave will begin receiving data after the

acknowledge (Figure 15-19).

FIGURE 15-19: GENERAL CALL ADDRESS SEQUENCE (7 OR 10-BIT MODE)

SDA

SCL

SSPIF (PIR2<7>)

BF (SSPSTAT<0>)

SSPOV (SSPCON1<6>)

Cleared in software

SSPBUF is read

R/W = 0

ACK

General Call Address

Address is compared to General Call Address

GCEN (SSPCON2<7>)

Receiving data

ACK

after ACK, set interrupt

PIC17C752-08/P Datasheet(PDF) 139 Page - Microchip Technology

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