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Bit 0: STF
0
1
Serial Data Register U (SDRU)
Bit
SDRU7
Initial value
Undefined Undefined Undefined Undefined Undefined Undefined Undefined Undefined
Read/Write
R/W
SDRU is an 8-bit read/write register. It is used as the data register for the upper 8 bits in 16-bit
transfer (SDRL is used for the lower 8 bits).
Data written to SDRU is output to SDRL starting from the least significant bit (LSB). This data is
then replaced by LSB-first data input at pin SI
significant bit (MSB) toward the LSB.
SDRU must be written or read only after data transmission or reception is complete. If this register
is written or read while a data transfer is in progress, the data contents are not guaranteed.
The SDRU value upon reset is not fixed.
Serial Data Register L (SDRL)
Bit
SDRL7
Initial value
Undefined Undefined Undefined Undefined Undefined Undefined Undefined Undefined
Read/Write
R/W
SDRL is an 8-bit read/write register. It is used as the data register in 8-bit transfer, and as the data
register for the lower 8 bits in 16-bit transfer (SDRU is used for the upper 8 bits).
In 8-bit transfer, data written to SDRL is output from pin SO
(LSB). This data is than replaced by LSB-first data input at pin SI
direction from the most significant bit (MSB) toward the LSB.
In 16-bit transfer, operation is the same as for 8-bit transfer, except that input data is fed in via
SDRU.
216
Description
Read
Indicates that transfer is stopped
Write
Invalid
Read
Indicates transfer in progress
Write
Starts a transfer operation
7
6
SDRU6
SDRU5
R/W
R/W
7
6
SDRL6
SDRL5
R/W
R/W
5
4
SDRU4
SDRU3
R/W
R/W
, which is shifted in the direction from the most
1
5
4
SDRL4
SDRL3
R/W
R/W
starting from the least significant bit
1
3
2
SDRU2
SDRU1
R/W
R/W
3
2
SDRL2
SDRL1
R/W
R/W
, which is shifted in the
1
(initial value)
1
0
SDRU0
R/W
1
0
SDRL0
R/W
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