Chapter 16 Serial Peripheral Interface (S12SPIV4)
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 729

Figure 16-12. SPI Clock Format 1 (CPHA = 1)

The SS line can remain active low between successive transfers (can be tied low at all times). This formatis sometimes preferred in systems having a single fixed master and a single slave that drive the MISO dataline. Back-to-back transfers in master modeIn master mode, if a transmission has completed and a new data byte is available in the SPI dataregister, this byte is sent out immediately without a trailing and minimum idle time.The SPI interrupt request flag (SPIF) is common to both the master and slave modes. SPIF gets set onehalf SCK cycle after the last SCK edge.
tLtT
for tT
, tl, tL
Minimum 1/2 SCK
tItL
If next transfer begins here
Begin End
SCK (CPOL = 0)
SAMPLE I
CHANGE O
SEL SS (O)
Transfer
SCK (CPOL = 1)
MSB first (LSBFE = 0):
LSB first (LSBFE = 1):
MSB
LSB
LSB
MSB
Bit 5
Bit 2
Bit 6
Bit 1
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
CHANGE O
SEL SS (I)
MOSI pin
MISO pin
Master only
MOSI/MISO
tL = Minimum leading time before the first SCK edge, not required for back-to-back transfers
tT = Minimum trailing time after the last SCK edge
tI = Minimum idling time between transfers (minimum SS high time), not required for back-to-back transfers
1 234 56 78910111213141516SCK Edge Number
End of Idle State Begin of Idle State