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Z51F6412
Product Specification
PS030302-0212
P R E L I M I N A R Y
96
11.7.3 Clock Generation
The Clock generation logic generates the base clock for the Transmitter and Receiver. The USART
supports four modes of clock operation and those are Normal Asynchronous, Double Speed
Asynchronous, Master Synchronous and Slave Synchronous. The clock generation scheme for
Master SPI and Slave SPI mode is the same as Master Synchronous and Slave Synchronous
operation mode. The UMSELn bit in UCTRLx1 register selects between asynchronous and
synchronous operation. Asynchronous Double Speed mode is controlled by the U2X bit in the
UCTRLx2 register. The MASTER bit in UCTRLx2 register controls whether the clock source is internal
(Master mode, output port) or external (Slave mode, input port). The XCK pin is only active when the
USART operates in Synchronous or SPI mode.
Table below contains equations for calculating the baud rate (in bps).
Table 11-13 Equations for Calculating Baud Rate Register Setting
Operating Mode
Equation for Calculating Baud Rate
Asynchronous Normal Mode (U2X=0)
Baud Rate
fSCLK
16 UBAUDx
1
Asynchronous Double Speed Mode (U2X=1)
Baud Rate
fSCLK
8 UBAUDx
1
Synchronous or SPI Master Mode
Baud Rate
fSCLK
2 UBAUDx
1
XCK
Prescaling
Up-Counter
UBAUD
/2
/8
Sync Register
M
U
X
M
U
X
M
U
X
M
U
X
/2
Edge
Detector
SCLK
f
SCLK
(UBAUD+1)
txclk
rxclk
UMSEL0
U2X
MASTER
UCPOL
Figure 11-23 Clock Generation Block Diagram