PIC16LF720_11 Datasheet, PDF (145/244 Pages) Microchip Technology – 20-Pin Flash Microcontrollers with nanoWatt XLP Technology

PIC16(L)F720/721
17.1.2.4 Slave Select Operation
The SS pin allows Synchronous Slave mode operation.
The SPI must be in Slave mode with SS pin control
enabled (SSPM<3:0> = 0100). The associated TRIS bit
for the SS pin must be set, making SS an input.
In Slave Select mode, when:
• SS = 0, The device operates as specified in
Section 17.1.2 “Slave Mode”.
• SS = 1, The SPI module is held in Reset and the
SDO pin will be tri-stated.
Note 1: When the SPI is in Slave mode with SS
pin control enabled (SSPM<3:0> = 0100),
the SPI module will reset if the SS pin is
driven high.
2: If the SPI is used in Slave mode with CKE
set, the SS pin control must be enabled.
When the SPI module resets, the bit counter is cleared
to ‘0’. This can be done by either forcing the SS pin to
a high level or clearing the SSPEN bit. Figure 17-6
shows the timing waveform for such a synchronization
event.
Note:
SSPSR must be reinitialized by writing to
the SSPBUF register before the data can
be clocked out of the slave again.
17.1.2.5 Sleep in Slave Mode
While in Sleep mode, the slave can transmit/receive
data. The SPI Transmit/Receive Shift register operates
asynchronously to the device on the externally supplied
clock source. This allows the device to be placed in
Sleep mode and data to be shifted into the SPI Trans-
mit/Receive Shift register. When all 8 bits have been
received, the SSP Interrupt Flag bit will be set and, if
enabled, will wake the device from Sleep.
FIGURE 17-6:
SLAVE SELECT SYNCHRONIZATION WAVEFORM
SS
SCK
(CKP = 0
CKE = 0)
SCK
(CKP = 1
CKE = 0)
Write to
SSPBUF
SDO
SDI
(SMP = 0)
Input
Sample
(SMP = 0)
SSPIF
Interrupt
Flag
SSPSR to
SSPBUF
bit 7
bit 6
bit 7
SSPSR must be reinitialized by writing to
the SSPBUF register before the data can
be clocked out of the slave again.
bit 7
bit 0
bit 0
bit 7
 2011 Microchip Technology Inc.
Preliminary
DS41430B-page 145