CHAPTER 8 CLOCKED SERIAL INTERFACE UNIT (CSI)
User’s Manual U14272EJ3V0UM
157
8.2.2 SCK phase and CSI transfer timing
The external master drives SCK and SI and samples data driven on SO. The CSI supports 4 basic operating
modes of SCK depending on the settings of CKPOL and CKMD bits. These are illustrated in the following figure.
Figure 8-1. SCK and SI/SO Relationship
(a) When CKMD bit = 0
SCK (input)
(when CKPOL = 0)
SCK (input)
(when CKPOL = 1)
SO (output)
SI (input)
Undefined
D7
D6
D0
D5
D4
D3
D2
D1
(b) When CKMD bit = 1
SCK (input)
(when CKPOL = 0)
SCK (input)
(when CKPOL = 1)
SO (output)
SI (input)
Undefined
D7
D6
D0
D5
D4
D3
D2
D1
Caution When the CKMD bit is set to 1, the next byte data is output during the latter half of the cycle for
the eighth bit of a transmit data.
This figure illustrates CSI cycles when the FRM input is disabled (FRMEN bit = 0) or configured to provide
direction control (FRMEN bit = 1 and FRMMD bit = 0). When FRMEN bit = 1 and FRMMD bit = 1, SO is driven as
high impedance during a high level input to FRM.
In addition, this figure illustrates the CSI cycles when bit 7 of a data is transmitted or received first (i.e. when the
LSBMSB bit of the CSIMODE register = 0).