pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 163

• Manufacturer Part Number: pc87591l
• Description: Lpc Mobile Embedded Controllers
• Manufacturer: National Semiconductor Corporation

Revision 1.07
Embedded Controller Modules
The baud rate register is programed with a baud rate divisor of 4 (N = baud rate divisor +1). This produces a baud clock of:
Note that the percent error is much lower than would be possible without the non-integer pre-scaler factor. Refer to the table
below for more examples.
Calculating the Baud Rate in Synchronous Mode
The equation for calculating the baud rate is:
where:
The same procedure is used for determining the values of N and P, as in Asynchronous mode. However, non-integer pre-
scale values are not allowed.
BR is the baud rate
SYS_CLK is the system clock
N is the value of the baud rate divisor + 1
P is the pre-scaler divide factor selected by the value in the PSR register
BR = (5x10
% error = (9615.385-9600)/9600 = 0.16
BR = SYS_CLK/(2xNxP)
6
System Clock
)/(16x5x6.5) = 9615.385
10 MHz
20 MHz
4 MHz
5 MHz
Baud Rate
Desired
19200
19200
9600
9600
(Continued)
N
2
5
5
5
163
6.5
6.5
13
13
P
Actual Baud Rate
19230.769
19230.769
9615.385
9615.385
Percent Error
0.16
0.16
0.16
0.16
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