PIC16F87 Datasheet, PDF (95/214 Pages) Microchip Technology – 18/20/28-Pin Enhanced FLASH Microcontrollers with nanoWatt Technology

10.3.1.1 Addressing
Once the SSP module has been enabled, it waits for a
START condition to occur. Following the START condi-
tion, the eight bits are shifted into the SSPSR register.
All incoming bits are sampled with the rising edge of the
clock (SCL) line. The value of register SSPSR<7:1> is
compared to the value of the SSPADD register. The
address is compared on the falling edge of the eighth
clock (SCL) pulse. If the addresses match, and the BF
and SSPOV bits are clear, the following events occur:
a) The SSPSR register value is loaded into the
SSPBUF register.
b) The buffer full bit, BF, is set.
c) An ACK pulse is generated.
d) SSP interrupt flag bit, SSPIF (PIR1<3>), is set
(interrupt is generated if enabled) - on the falling
edge of the ninth SCL pulse.
In 10-bit Address mode, two address bytes need to be
received by the slave device. The five Most Significant
bits (MSbs) of the first address byte specify if this is a
10-bit address. Bit R/W (SSPSTAT<2>) must specify a
write so the slave device will receive the second
address byte. For a 10-bit address, the first byte would
equal ‘1111 0 A9 A8 0’, where A9 and A8 are the
two MSbs of the address.
The sequence of events for 10-bit address is as
follows, with steps 7- 9 for slave transmitter:
1. Receive first (high) byte of address (bits SSPIF,
BF, and bit UA (SSPSTAT<1>) are set).
2. Update the SSPADD register with second (low)
byte of address (clears bit UA and releases the
SCL line).
3. Read the SSPBUF register (clears bit BF) and
clear flag bit SSPIF.
4. Receive second (low) byte of address (bits
SSPIF, BF, and UA are set).
5. Update the SSPADD register with the first (high)
byte of Address, if match releases SCL line, this
will clear bit UA.
6. Read the SSPBUF register (clears bit BF) and
clear flag bit SSPIF.
7. Receive Repeated START condition.
8. Receive first (high) byte of address (bits SSPIF
and BF are set).
9. Read the SSPBUF register (clears bit BF) and
clear flag bit SSPIF.
PIC16F87/88
10.3.1.2 Reception
When the R/W bit of the address byte is clear and an
address match occurs, the R/W bit of the SSPSTAT
register is cleared. The received address is loaded into
the SSPBUF register.
When the address byte overflow condition exists, then
a no Acknowledge (ACK) pulse is given. An overflow
condition is indicated if either bit, BF (SSPSTAT<0>), is
set or bit, SSPOV (SSPCON<6>), is set.
An SSP interrupt is generated for each data transfer
byte. Flag bit, SSPIF (PIR1<3>), must be cleared in
software. The SSPSTAT register is used to determine
the status of the byte.
10.3.1.3 Transmission
When the R/W bit of the incoming address byte is set
and an address match occurs, the R/W bit of the
SSPSTAT register is set. The received address is
loaded into the SSPBUF register. The ACK pulse will
be sent on the ninth bit, and pin RB4/SCK/SCL is held
low. The transmit data must be loaded into the
SSPBUF register, which also loads the SSPSR regis-
ter. Then, pin RB4/SCK/SCL should be enabled by set-
ting bit CKP (SSPCON<4>). The master device must
monitor the SCL pin prior to asserting another clock
pulse. The slave devices may be holding off the master
device by stretching the clock. The eight data bits are
shifted out on the falling edge of the SCL input. This
ensures that the SDA signal is valid during the SCL
high time (Figure 10-7).
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 master
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 device, the slave logic is reset (resets
SSPSTAT register) and the slave device 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 reg-
ister. Then, pin RB4/SCK/SCL should be enabled by
setting bit CKP.
 2003 Microchip Technology Inc.
Preliminary
DS30487B-page 93