PIC18F44J50-I Datasheet, PDF (271/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

PIC18F46J50 FAMILY
19.3.1 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.
Since the SSPxBUF register is double-buffered for
receive operations, using read-modify-write instruc-
tions that target SSPxBUF, twice per instruction, such
as BCF, COMF, etc., will not work. SSPxBUF may be
read or written using standard instructions that target
the register, once per instruction, such as MOVWF, MOVF
(dest = WREG) and MOVFF.
Similarly, when debugging under an In-Circuit Debug-
ger, performing actions that cause reads of SSPxBUF
(ex: debug watch) can consume data that the
application code was expecting to receive.
REGISTER 19-1: SSPxSTAT: MSSPx STATUS REGISTER (SPI MODE) (ACCESS FC7h, F73h)
R/W-0
R/W-0
R-0
R-0
R-0
R-0
R-0
R-0
SMP
CKE⁽¹⁾
D/A
P
S
R/W
UA
BF
bit 7
bit 0
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
x = Bit is unknown
bit 7
SMP: Sample bit
SPI Master mode:
1 = Input data is sampled at the end of data output time
0 = Input data is 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 I²C™ mode only.
bit 4
P: Stop bit
Used in I²C mode only; this bit is cleared when the MSSP module is disabled, SSPEN is cleared.
bit 3
S: Start bit
Used in I²C mode only.
bit 2
R/W: Read/Write Information bit
Used in I²C mode only.
bit 1
UA: Update Address bit
Used in I²C mode only.
bit 0
BF: Buffer Full Status bit
1 = Receive is complete, SSPxBUF is full
0 = Receive is not complete, SSPxBUF is empty
Note 1: Polarity of clock state is set by the CKP bit (SSPxCON1<4>).
 2011 Microchip Technology Inc.
DS39931D-page 271