PIC16F193X Datasheet, PDF (286/418 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

PIC16F193X/LF193X
22.3.6 SLAVE MODE
In Slave mode, the data is transmitted and received as
external clock pulses appear on SCK. When the last
bit is latched, the SSPIF interrupt flag bit is set.
Before enabling the module in SPI Slave mode, the clock
line must match the proper Idle state. The clock line can
be observed by reading the SCK pin. The Idle state is
determined by the CKP bit of the SSPCON1 register.
While in Slave mode, the external clock is supplied by
the external clock source on the SCK pin. This external
clock must meet the minimum high and low times as
specified in the electrical specifications.
While in Sleep mode, the slave can transmit/receive
data. The shift register is clocked from the SCK pin
input and when a byte is received, the device will gen-
erate an interrupt. If enabled, the device will wake-up
from Sleep.
22.3.6.1 Buffer Overwrite Enable
In SPI daisy-chained configurations only the most
recent byte on the bus is required by the slave. Setting
the BOEN bit of the SSPCON3 register will enable
writes to the SSPBUF register, even if the previous
byte has not been read. Allowing the software to
ignore data that may not apply to it.
22.3.7 SLAVE SELECT SYNCHRONIZATION
The SS pin allows a Synchronous Slave mode. The
SPI must be in Slave mode with SS pin control enabled
(SSPCON1<3:0> = 0100).
When the SS pin is low, transmission and reception are
enabled and the SDO pin is driven.
When the SS pin goes high, the SDO pin is no longer
driven, even if in the middle of a transmitted byte and
becomes a floating output. External pull-up/pull-down
resistors may be desirable depending on the applica-
tion.
Note 1: When the SPI is in Slave mode with SS pin
control enabled (SSPCON1<3:0> =
0100), the SPI module will reset if the SS
pin is set to VDD.
2: When the SPI is used in Slave mode with
CKE set; the user must enable SS pin
control.
3: While operated in SPI Slave mode the
SMP bit of the SSPSTAT register must
remain clear.
When the SPI module resets, the bit counter is forced
to ‘0’. This can be done by either forcing the SS pin to
a high level or clearing the SSPEN bit.
FIGURE 22-6:
SLAVE SELECT SYNCRONIZATION WAVEFORM
SS
SCK
(CKP = 0
CKE = 0)
SCK
(CKP = 1
CKE = 0)
Write to
SSPBUF
SSPBUF to
SSPSR
Shift register SSPSR
and bit count are reset
SDO
SDI
Input
Sample
SSPIF
Interrupt
Flag
SSPSR to
SSPBUF
bit 7
bit 6
bit 7
bit 7 bit 6
bit 7
bit 0
bit 0
DS41364A-page 284
Preliminary
© 2008 Microchip Technology Inc.