PIC18F97J60 Datasheet, PDF (265/474 Pages) Microchip Technology – 64/80/100-Pin, High-Performance, 1 Mbit Flash Microcontrollers with Ethernet

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19.3.8 OPERATION IN POWER-MANAGED
MODES
In SPI Master mode, module clocks may be operating
at a different speed than when in full power mode. In
the case of Sleep mode, all clocks are halted.
In Idle modes, a clock is provided to the peripherals.
That clock should be from the primary clock source, the
secondary clock (Timer1 oscillator at 32.768 kHz) or
the INTRC source. See Section 2.7 “Clock Sources
and Oscillator Switching” for additional information.
In most cases, the speed that the master clocks SPI
data is not important; however, this should be
evaluated for each system.
If MSSP interrupts are enabled, they can wake the
controller from Sleep mode, or one of the Idle modes,
when the master completes sending data. If an exit
from Sleep or Idle mode is not desired, MSSP
interrupts should be disabled.
If the Sleep mode is selected, all module clocks are
halted and the transmission/reception will remain in
that state until the devices wakes. After the device
returns to Run mode, the module will resume
transmitting and receiving data.
In SPI Slave mode, the SPI Transmit/Receive Shift
register operates asynchronously to the device. This
allows the device to be placed in any power-managed
mode and data to be shifted into the SPI
Transmit/Receive Shift register. When all 8 bits have
been received, the MSSP interrupt flag bit will be set
and if enabled, will wake the device.
19.3.9 EFFECTS OF A RESET
A Reset disables the MSSP module and terminates the
current transfer.
19.3.10 BUS MODE COMPATIBILITY
Table 19-1 shows the compatibility between the
standard SPI modes and the states of the CKP and
CKE control bits.
TABLE 19-1: SPI BUS MODES
Standard SPI Mode
Terminology
Control Bits State
CKP
CKE
0, 0
0
1
0, 1
0
0
1, 0
1
1
1, 1
1
0
There is also an SMP bit which controls when the data
is sampled.
19.3.11 SPI CLOCK SPEED AND MODULE
INTERACTIONS
Because MSSP1 and MSSP2 are independent
modules, they can operate simultaneously at different
data rates. Setting the SSPM3:SSPM0 bits of the
SSPxCON1 register determines the rate for the
corresponding module.
An exception is when both modules use Timer2 as a
time base in Master mode. In this instance, any
changes to the Timer2 operation will affect both MSSP
modules equally. If different bit rates are required for
each module, the user should select one of the other
three time base options for one of the modules.
© 2006 Microchip Technology Inc.
Advance Information
DS39762A-page 263