at89s8253-24psu ATMEL Corporation, at89s8253-24psu Datasheet - Page 27

• Manufacturer Part Number: at89s8253-24psu
• Description: At89s8253 8-bit Microcontroller With 12k Bytes Flash And 2k Bytes Eeprom
• Manufacturer: ATMEL Corporation

3286K–MICRO–12/06
Figure 14-3. 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
Figure 14-4
CPOL, and SPR should be set up before the interface is enabled, and the master device should
be enabled before the slave device(s).
Table 14-4.
Symbol
t
t
t
t
t
t
t
t
t
t
Transmit
CLCL
SCK
SHSL
SLSH
SR
SF
SIS
SIH
SOH
SOV
Serial In
Byte
and
8
SPI Master Characteristics
Parameter
Oscillator Period
Serial Clock Cycle Time
Clock High Time
Clock Low Time
Rise Time
Fall Time
Serial Input Setup Time
Serial Input Hold Time
Serial Output Hold Time
Serial Output Valid Time
Figure
MUX
8
2:1
14-5. To prevent glitches on SCK from disrupting the interface, CPHA,
8
Parallel Master
Serial Master
(Write Buffer)
D
CLK
D
CLK
LATCH
LATCH
Q
Q
7
t
t
SCK
SCK
4t
41.6
Min
/2 - 25
/2 - 25
10
10
CLCL
MUX
2:1
8
Parallel Slave
Serial Slave
Max
(Read Buffer)
25
10
35
25
D
CLK
D
CLK
LATCH
LATCH
AT89S8253
Q
Q
8
Serial Out
Units
Receive
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Byte
27