
NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
- 538 -
Revision V1.30
NUC97
0
T
E
CHNIC
A
L
RE
F
E
RE
N
CE
MA
NUA
L
These four bits provide the configuration of suspend interval between two successive transmit/receive
in a transfer. The default value is 0x0. When CNTRL[Tx_NUM] = 00, setting this field has no effect on
transfer. The desired interval is obtained according to the following equation (from the last falling edge
of current sclk to the first rising edge of next sclk).
(CNTRL[SLEEP] + 2)*period of SCLK
Clock Divider
The value of DIVIDER (DIVIDER[15:0]) is the frequency divider of the system clock pclk to generate
the serial clock on the output mw_sclk_o. The desired frequency is obtained according to the following
equation:
2
*
1
DIVIDER
f
f
pclk
sclk
Auto Select
The auto select function is controlled in ASS bit (SSR[3]).
If this bit is cleared, slave select signals are asserted and de-asserted by setting and clearing related
bits in SSR register.
If this bit is set, mw_ss_o signals are generated automatically. It means that device/slave select signal,
which is set in SSR register is asserted by the SPI controller when transmit/receive is started by
setting CNTRL[GO_BUSY], and is de-asserted after every transmit/receive is finished.
Slave Select
The SPI controller can drive up to two off-chip slave devices on SS[1:0] (SSR[1:0]) through the slave
select output pins mw_ss_o[1:0]. The active state of slave select signal can be programmed to low or
high active in SS_LVL bit (SSR[2]). The selection of slave select conditions depends on what type of
peripheral slave/master device is connected.
SPI Timing Diagram
5.19.5.2
MSB
(Tx[7])
LSB
(Tx[0])
MSB
(Rx[7])
LSB
(Rx[0])
mw_ss_o
mw_sclk_o
mw_so_o
mw_si_i
CNTRL[LSB]=0, CNTRL[Tx_NUM]=0x0, CNTRL[Tx_BIT_LEN]=0x08,
CNTRL[Tx_NEG]=1, CNTRL[Rx_NEG]=0, SSR[SS_LVL]=0
Tx[6]
Tx[5]
Tx[4]
Tx[3]
Tx[2]
Tx[1]
Rx[6]
Rx[5]
Rx[4]
Rx[3]
Rx[2]
Rx[1]
Figure 5.19-2 Normal SPI Timing