Microchip Technology AC244045 Data Sheet
PIC16F72X/PIC16LF72X
DS41341E-page 178
© 2009 Microchip Technology Inc.
17.2.2
START AND STOP CONDITIONS
During times of no data transfer (Idle time), both the
clock line (SCL) and the data line (SDA) are pulled high
through external pull-up resistors. The Start and Stop
conditions determine the start and stop of data trans-
mission. The Start condition is defined as a high-to-low
transition of the SDA line while SCL is high. The Stop
condition is defined as a low-to-high transition of the
SDA line while SCL is high.
clock line (SCL) and the data line (SDA) are pulled high
through external pull-up resistors. The Start and Stop
conditions determine the start and stop of data trans-
mission. The Start condition is defined as a high-to-low
transition of the SDA line while SCL is high. The Stop
condition is defined as a low-to-high transition of the
SDA line while SCL is high.
Figure 17-9 shows the Start and Stop conditions. A
master device generates these conditions for starting
and terminating data transfer. Due to the definition of
the Start and Stop conditions, when data is being trans-
mitted, the SDA line can only change state when the
SCL line is low.
master device generates these conditions for starting
and terminating data transfer. Due to the definition of
the Start and Stop conditions, when data is being trans-
mitted, the SDA line can only change state when the
SCL line is low.
FIGURE 17-9:
START AND STOP CONDITIONS
17.2.3
ACKNOWLEDGE
After the valid reception of an address or data byte, the
hardware automatically will generate the Acknowledge
(ACK) pulse and load the SSPBUF register with the
received value currently in the SSPSR register. There
are certain conditions that will cause the SSP module
not to generate this ACK pulse. They include any or all
of the following:
hardware automatically will generate the Acknowledge
(ACK) pulse and load the SSPBUF register with the
received value currently in the SSPSR register. There
are certain conditions that will cause the SSP module
not to generate this ACK pulse. They include any or all
of the following:
• The Buffer Full bit, BF of the SSPSTAT register,
was set before the transfer was received.
• The SSP Overflow bit, SSPOV of the SSPCON
register, was set before the transfer was received.
• The SSP Module is being operated in Firmware
Master mode.
In such a case, the SSPSR register value is not loaded
into the SSPBUF, but bit SSPIF of the PIR1 register is
set. Table 17-2 shows the results of when a data
transfer byte is received, given the status of bits BF and
SSPOV. Flag bit BF is cleared by reading the SSPBUF
register, while bit SSPOV is cleared through software.
into the SSPBUF, but bit SSPIF of the PIR1 register is
set. Table 17-2 shows the results of when a data
transfer byte is received, given the status of bits BF and
SSPOV. Flag bit BF is cleared by reading the SSPBUF
register, while bit SSPOV is cleared through software.
TABLE 17-2:
DATA TRANSFER RECEIVED BYTE ACTIONS
SDA
SCL
P
Stop
Condition
S
Start
Condition
Change of
Data Allowed
Change of
Data Allowed
Status Bits as Data
Transfer is Received
SSPSR
→ SSPBUF
Generate ACK
Pulse
Set bit SSPIF
(SSP Interrupt occurs
if enabled)
BF
SSPOV
0
0
Yes
Yes
Yes
1
0
No
No
Yes
1
1
No
No
Yes
0
1
No
No
Yes
Note 1:
Shaded cells show the conditions where the user software did not properly clear the overflow condition.