Datasheet

 2010 Microchip Technology Inc. Preliminary DS39974A-page 293
PIC18F47J13 FAMILY
20.3.1 REGISTERS
Each MSSP module has four registers for SPI mode
operation. These are:
• MSSPx Control Register 1 (SSPxCON1)
• MSSPx Status Register (SSPxSTAT)
• Serial Receive/Transmit Buffer Register
(SSPxBUF)
• MSSPx Shift Register (SSPxSR) – Not directly
accessible
SSPxCON1 and SSPxSTAT are the control and status
registers in SPI mode operation. The SSPxCON1
register is readable and writable. The lower six bits of
the SSPxSTAT are read-only. The upper two bits of the
SSPxSTAT are read/write.
SSPxSR is the shift register used for shifting data in or
out. SSPxBUF is the buffer register to which data
bytes are written to or read from.
In receive operations, SSPxSR and SSPxBUF
together, create a double-buffered receiver. When
SSPxSR receives a complete byte, it is transferred to
SSPxBUF and the SSPxIF interrupt is set.
During transmission, the SSPxBUF is not
double-buffered. A write to SSPxBUF will write to both
SSPxBUF and SSPxSR.
Note: Because the SSPxBUF register is
double-buffered, using read-modify-write
instructions such as BCF, COMF, etc., will not
work.
Similarly, when debugging under an
in-circuit debugger, performing actions that
cause reads of SSPxBUF (mouse hover-
ing, watch, etc.) can consume data that the
application code was expecting to receive.
REGISTER 20-1: SSPxSTAT: MSSPx STATUS REGISTER (SPI MODE) (ACCESS 1, FC7h; 2, F73h)
R/W-1 R/W-1 R-1 R-1 R-1 R-1 R-1 R-1
SMP CKE
(1)
D/A PSR/WUA BF
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 7 SMP: Sample bit
SPI Master mode:
1 = Input data sampled at the end of data output time
0 = Input data sampled at the middle of data output time
SPI Slave mode:
SMP must be cleared when SPI is used in Slave mode.
bit 6 CKE: SPI Clock Select bit
(1)
1 = Transmit occurs on transition from active to Idle clock state
0 = Transmit occurs on transition from Idle to active clock state
bit 5 D/A
: Data/Address bit
Used in I
2
C™ mode only.
bit 4 P: Stop bit
Used in I
2
C mode only; this bit is cleared when the MSSP module is disabled, SSPEN is cleared.
bit 3 S: Start bit
Used in I
2
C mode only.
bit 2 R/W: Read/Write Information bit
Used in I
2
C mode only.
bit 1 UA: Update Address bit
Used in I
2
C mode only.
bit 0 BF: Buffer Full Status bit
1 = Receive complete, SSPxBUF is full
0 = Receive not complete, SSPxBUF is empty
Note 1: Polarity of the clock state is set by the CKP bit (SSPxCON1<4>).