Spi chip select register – Rainbow Electronics AT75C220 User Manual
Page 138
AT75C220
138
SPI Chip Select Register
Register Name:SP_CSR0
Access Type:Read/write
Reset Value:0x0
•
CPOL: Clock Polarity
0 = The inactive state value of SPCK is logic level zero.
1 = The inactive state value of SPCK is logic level one.
CPOL is used to determine the inactive state value of the serial clock (SPCK). It is used with NCPHA to produce a
desired clock/data relationship between master and slave devices.
•
NCPHA: Clock Phase
0 = Data is changed on the leading edge of SPCK and captured on the following edge of SPCK.
1 = Data is captured on the leading edge of SPCK and changed on the following edge of SPCK.
NCPHA determines which edge of SPCK causes data to change and which edge causes data to be captured. NCPHA
is used with CPOL to produce a desired clock/data relationship between master and slave devices.
•
BITS: Bits Per Transfer
The BITS field determines the number of data bits transferred. Reserved values should not be used.
31
30
29
28
27
26
25
24
DLYBCT
23
22
21
20
19
18
17
16
DLYBS
15
14
13
12
11
10
9
8
SCBR
7
6
5
4
3
2
1
0
BITS
–
–
NCPHA
CPOL
BITS[3:0]
Bits per
Transfer
BITS[3:0]
Bits per
Transfer
0000
8
1000
16
0001
9
1001
Reserved
0010
10
1010
Reserved
0011
11
1011
Reserved
0100
12
1100
Reserved
0101
13
1101
Reserved
0110
14
1110
Reserved
0111
15
1111
Reserved