at89lp2052-20xi ATMEL Corporation, at89lp2052-20xi Datasheet - Page 46

• Manufacturer Part Number: at89lp2052-20xi
• Description: At89lp2052 8-bit Microcontroller With 2/4-kbyte Flash
• Manufacturer: ATMEL Corporation

19.3
46
Serial Clock Generator
AT89LP2052/LP4052
Figure 19-3. SPI Shift Register Diagram
The CPHA (Clock PHAse), CPOL (Clock POLarity), and SPR (Serial Peripheral clock Rate =
baud rate) bits in SPCR control the shape and rate of SCK. The two SPR bits provide four possi-
ble clock rates when the SPI is in master mode. In slave mode, the SPI will operate at the rate of
the incoming SCK as long as it does not exceed the maximum bit rate. There are also four pos-
sible combinations of SCK phase and polarity with respect to the serial data. CPHA and CPOL
determine which format is used for transmission. The SPI data transfer formats are shown in
Figures 19-4 and
CPOL, and SPR should be set up before the interface is enabled, and the master device should
be enabled before the slave device(s).
Transmit
Serial In
Byte
8
and 19-5. To prevent glitches on SCK from disrupting the interface, CPHA,
MUX
8
2:1
8
Parallel Master
Serial Master
(Write Buffer)
D
CLK
D
CLK
LATCH
LATCH
Q
Q
7
MUX
2:1
8
Parallel Slave
Serial Slave
(Read Buffer)
D
CLK
D
CLK
LATCH
LATCH
Q
Q
3547H–MICRO–5/07
8
Serial Out
Receive
Byte