PIC16F720-ESLASHML datasheet(145/244 Pages) MICROCHIP

145 / 244 page

 2010 Microchip Technology Inc.

DS41430A-page 145

PIC16F/LF720/721

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.

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.

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

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.

Note:

SSPSR must be reinitialized by writing to

the SSPBUF register before the data can

be clocked out of the slave again.

SCK

(CKP = 1

SCK

(CKP = 0

Input

Sample

SDI

bit 7

SDO

bit 7

bit 6

bit 7

SSPIF

Interrupt

(SMP = 0)

CKE = 0)

(SMP = 0)

Write to

SSPBUF

SSPSR to

SSPBUF

Flag

bit 0

bit 7

bit 0

SSPSR must be reinitialized by writing to

the SSPBUF register before the data can

be clocked out of the slave again.

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