254
MC97F60128
ABOV Semiconductor Co., Ltd.
11.13.4 USI0/1 Clock Generation
Figure 11.63
Clock Generation Block Diagram (USIn, where n = 0 and 1)
The clock generation logic generates the base clock for the transmitter and receiver. The USI0/1 supports four modes
of clock operation and those are normal asynchronous, double speed asynchronous, master synchronous and slave
synchronous mode. The clock generation scheme for master SPI and slave SPI mode is the same as master
synchronous and slave synchronous operation mode. The USInMS[1:0] bits in USInCR1 register selects
asynchronous or synchronous operation. Asynchronous double speed mode is controlled by the DBLSn bit in the
USInCR2 register. The MASTERn bit in USInCR3 register controls whether the clock source is internal (master mode,
output pin) or external (slave mode, input pin). The SCKn pin is active only when the USI0/1 operates in synchronous
or SPI mode.
Following table shows the equations for calculating the baud rate (in bps).
Operating Mode
Equation for Calculating Baud Rate
Asynchronous Normal Mode (DBLSn=0)
Baud Rate =
fx
16( 1)
Asynchronous Double Speed Mode (DBLSn=1)
Baud Rate =
fx
8( 1)
Synchronous or SPI Master Mode
Baud Rate =
fx
2( 1)
Table 11-22
Equations for Calculating USI0/1 Baud Rate Register Setting
SCKn
Prescaling
Up-Counter
USInBD
/2
/8
Sync Register
M
U
X
M
U
X
M
U
X
M
U
X
/2
Edge
Detector
SCLK
f
SCLK
(1)
txclk
rxclk
USInMS[1:0]
DBLSn
MASTERn
CPOLn
Summary of Contents for MC97F60128
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