127
MC95FG308 / MC95FG208
ABOV Semiconductor Co., Ltd.
11.7.4 External Clock (XCK)
External clocking is used by the synchronous or SPI slave modes of operation.
External clock input from the XCK pin is sampled by a synchronization logic to remove meta-stability. The output from
the synchronization logic must then pass through an edge detector before it can be used by the Transmitter and
Receiver. This process introduces a two CPU clock period delay and therefore the maximum frequency of the external
XCK pin is limited by the following equation.
fXCK =
fSCLK
4
where fXCK is the frequency of XCK and fSCLK is the frequency of main system clock (SCLK).
11.7.5 Synchronous mode Operation
When synchronous or SPI mode is used, the XCK pin will be used as either clock input (slave) or clock output
(master). The dependency between the clock edges and data sampling or data change is the same. The basic
principle is that data input on RXD (MISO in SPI mode) pin is sampled at the opposite XCK clock edge of the edge in
the data output on TXD (MOSI in SPI mode) pin is changed.
The UCPOL bit in UCTRLx1 register selects which XCK clock edge is used for data sampling and which is used for
data change. As shown in the figure below, when UCPOL is zero the data will be changed at rising XCK edge and
sampled at falling XCK edge.
Figure 11.41
Synchronous Mode XCKn Timing
XCK
TXD/RXD
UCPOL = 1
TXD/RXD
XCK
UCPOL = 0
Sample
Sample
Содержание MC95FG208 Series
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Страница 16: ...16 MC95FG308 MC95FG208 ABOV Semiconductor Co Ltd Figure 4 3 32 Pin LQFP Package...
Страница 17: ...17 MC95FG308 MC95FG208 ABOV Semiconductor Co Ltd Figure 4 4 28 Pin SOP Package...
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Страница 20: ...20 MC95FG308 MC95FG208 ABOV Semiconductor Co Ltd Figure 4 7 28 Pin TSSOP Package...
Страница 21: ...21 MC95FG308 MC95FG208 ABOV Semiconductor Co Ltd Figure 4 8 20 Pin SOP Package...
Страница 22: ...22 MC95FG308 MC95FG208 ABOV Semiconductor Co Ltd Figure 4 9 20 Pin TSSOP Package...
Страница 23: ...23 MC95FG308 MC95FG208 ABOV Semiconductor Co Ltd Figure 4 10 16 Pin SOP Package...
Страница 24: ...24 MC95FG308 MC95FG208 ABOV Semiconductor Co Ltd Figure 4 11 16 Pin TSSOP Package...