Datasheet

© 2009 Microchip Technology Inc. DS39689F-page 175
PIC18F2221/2321/4221/4321 FAMILY
18.3.8 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 INTOSC source. See Section 3.7 “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.
18.3.9 EFFECTS OF A RESET
A Reset disables the MSSP module and terminates the
current transfer.
18.3.10 BUS MODE COMPATIBILITY
Table 18-1 shows the compatibility between the
standard SPI modes and the states of the CKP and
CKE control bits.
TABLE 18-1: SPI BUS MODES
There is also an SMP bit which controls when the data
is sampled.
TABLE 18-2: REGISTERS ASSOCIATED WITH SPI OPERATION
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
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Reset
Values
on page
INTCON GIE/GIEH PEIE/GIEL
TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF 55
PIR1
PSPIF
(1)
ADIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF 58
PIE1
PSPIE
(1)
ADIE RCIE TXIE SSPIE CCP1IE TMR2IE TMR1IE 58
IPR1 PSPIP
(1)
ADIP RCIP TXIP SSPIP CCP1IP TMR2IP TMR1IP 58
TRISA TRISA7
(2)
TRISA6
(2)
PORTA Data Direction Control Register 58
TRISC PORTC Data Direction Control Register 58
SSPBUF MSSP Receive Buffer/Transmit Register 56
SSPCON1 WCOL SSPOV SSPEN CKP SSPM3 SSPM2 SSPM1 SSPM0 56
SSPSTAT SMP CKE
D/A P S R/W UA BF 56
Legend: Shaded cells are not used by the MSSP in SPI mode.
Note 1: These bits are unimplemented on 28-pin devices and read as ‘0’.
2: PORTA<7:6> and their direction bits are individually configured as port pins based on various primary
oscillator modes. When disabled, these bits read as ‘0’.