mc9s12xd256 Freescale Semiconductor, Inc, mc9s12xd256 Datasheet - Page 534

• Manufacturer Part Number: mc9s12xd256
• Description: Hcs12x Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Chapter 12 Serial Peripheral Interface (S12SPIV4)
The SS line can remain active low between successive transfers (can be tied low at all times). This format
is sometimes preferred in systems having a single fixed master and a single slave that drive the MISO data
line.
The SPI interrupt request flag (SPIF) is common to both the master and slave modes. SPIF gets set one
half SCK cycle after the last SCK edge.
534
•
End of Idle State
SCK Edge Number
SCK (CPOL = 0)
SCK (CPOL = 1)
SAMPLE I
MOSI/MISO
CHANGE O
CHANGE O
SEL SS (O)
Master only
SEL SS (I)
MOSI pin
MISO pin
Back-to-back transfers in master mode
In master mode, if a transmission has completed and a new data byte is available in the SPI data
register, this byte is sent out immediately without a trailing and minimum idle time.
MSB first (LSBFE = 0):
t
t
t
LSB first (LSBFE = 1):
L
T
I
= Minimum idling time between transfers (minimum SS high time), not required for back-to-back transfers
= Minimum leading time before the first SCK edge, not required for back-to-back transfers
= Minimum trailing time after the last SCK edge
t
L
1
MSB
LSB
2
Figure 12-12. SPI Clock Format 1 (CPHA = 1)
3
Begin
Bit 6
Bit 1
4
MC9S12XDP512 Data Sheet, Rev. 2.17
5
Bit 5
Bit 2
6
7
Bit 4
Bit 3
8
Transfer
9
Bit 3
Bit 4
10
11
Bit 2
Bit 5
12
13 14
Bit 1
Bit 6
End
15
MSB
LSB
16
t
T
Minimum 1/2 SCK
Freescale Semiconductor
Begin of Idle State
t
I
for t
T
t
L
, t
l
, t
L