MC68HC908GR16 Datasheet, PDF (197/276 Pages) Motorola, Inc – Microcontrollers

Functional Description
16.4 Functional Description
Figure 16-2 summarizes the SPI I/O registers and Figure 16-3 shows the structure of the SPI module.
The SPI module allows full-duplex, synchronous, serial communication between the MCU and peripheral
devices, including other MCUs. Software can poll the SPI status flags or SPI operation can be interrupt
driven.
If a port bit is configured for input, then an internal pullup device may be enabled for that port bit. See
12.4.3 Port C Input Pullup Enable Register.
The following paragraphs describe the operation of the SPI module.
Addr.
$0010
$0011
$0012
Register Name
SPI Control Register ^Read:
(SPCR) Write:
See page 212. _Reset:
SPI Status and Control ^Read:
Register (SPSCR) Write:
See page 213. _Reset:
SPI Data Register ^Read:
(SPDR) Write:
See page 215. _Reset:
Bit 7
SPRIE
0
SPRF
0
R7
T7
R
6
5
R
SPMSTR
0
ERRIE
1
OVRF
0
0
R6
R5
T6
T5
= Reserved
4
3
2
CPOL CPHA SPWOM
0
MODF
1
SPTE
0
MODFEN
0
1
0
R4
R3
R2
T4
T3
T2
Unaffected by reset
= Unimplemented
Figure 16-2. SPI I/O Register Summary
1
SPE
0
SPR1
0
R1
T1
Bit 0
SPTIE
0
SPR0
0
R0
T0
16.4.1 Master Mode
The SPI operates in master mode when the SPI master bit, SPMSTR, is set.
NOTE
Configure the SPI modules as master or slave before enabling them.
Enable the master SPI before enabling the slave SPI. Disable the slave SPI
before disabling the master SPI. See 16.13.1 SPI Control Register.
Only a master SPI module can initiate transmissions. Software begins the transmission from a master SPI
module by writing to the transmit data register. If the shift register is empty, the byte immediately transfers
to the shift register, setting the SPI transmitter empty bit, SPTE. The byte begins shifting out on the MOSI
pin under the control of the serial clock. See Figure 16-4.
The SPR1 and SPR0 bits control the baud rate generator and determine the speed of the shift register.
(See 16.13.2 SPI Status and Control Register.) Through the SPSCK pin, the baud rate generator of the
master also controls the shift register of the slave peripheral.
MC68HC908GR16 Data Sheet, Rev. 5.0
Freescale Semiconductor
197