PIC16F7X7
10.3.1
REGISTERS
The MSSP module has four registers for SPI mode
operation. These are:
•
•
•
•
MSSP Control Register (SSPCON)
MSSP Status Register (SSPSTAT)
Serial Receive/Transmit Buffer (SSPBUF)
MSSP Shift Register (SSPSR) – Not directly
accessible
SSPSR is the shift register used for shifting data in or
out. SSPBUF is the buffer register to which data bytes
are written to or read from.
In receive operations, SSPSR and SSPBUF together
create a double-buffered receiver. When SSPSR
receives a complete byte, it is transferred to SSPBUF
and the SSPIF interrupt is set.
During transmission, the SSPBUF is not double-
buffered. A write to SSPBUF will write to both SSPBUF
and SSPSR.
SSPCON and SSPSTAT are the control and status
registers in SPI mode operation. The SSPCON
register is readable and writable. The lower 6 bits of
the SSPSTAT are read-only. The upper two bits of the
SSPSTAT are read/write.
REGISTER 10-1:
SSPSTAT: MSSP STATUS (SPI MODE) REGISTER (ADDRESS 94h)
R/W-0
SMP
bit 7
R/W-0
CKE
R-0
D/A
R-0
P
R-0
S
R-0
R/W
R-0
UA
R-0
BF
bit 0
bit 7
SMP:
Sample bit
SPI Master mode:
1
= Input data sampled at end of data output time
0
= Input data sampled at middle of data output time
SPI Slave mode:
SMP must be cleared when SPI is used in Slave mode.
CKE:
SPI Clock Edge Select bit
1
= Transmit occurs on transition from active to Idle clock state
0
= Transmit occurs on transition from Idle to active clock state
Note:
Polarity of clock state is set by the CKP bit (SSPCON1<4>).
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
D/A:
Data/Address bit
Used in I
2
C mode only.
P:
Stop bit
Used in I
2
C mode only. This bit is cleared when the MSSP module is disabled, SSPEN is cleared.
S:
Start bit
Used in I
2
C mode only.
R/W:
Read/Write bit Information
Used in I
2
C mode only.
UA:
Update Address bit
Used in I
2
C mode only.
BF:
Buffer Full Status bit (Receive mode only)
1
= Receive complete, SSPBUF is full
0
= Receive not complete, SSPBUF is empty
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
DS30498C-page 94
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
