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XC161 Derivatives
Peripheral Units (Vol. 2 of 2)
Asynchronous/Synchronous Serial Interface (ASC)
User’s Manual
18-31
V2.2, 2004-01
ASC_X, V2.0
According to
a baudrate of 9600 bit/s is achieved when register ASCx_BG is
loaded with a value of 047
H
, assuming that
f
DIV
has been set to 11.0592 MHz.
also lists a divide factor d
f
which is defined with the following formula:
(18.2)
This divide factor d
f
defines a fixed relationship between the prescaler output frequency
f
DIV
and the baudrate to be detected during the Autobaud Detection operation. This
means, changing
f
DIV
results in a totally different baudrate table in means of baudrate
values. For the baudrates to be detected, the following relations are always valid:
Br0 =
f
DIV
/48
D
, Br1 =
f
DIV
/96
D
, … up to Br8 =
f
DIV
/9216
D
A requirement for detecting standard baudrates up to 230.400 kbit/s is the
f
DIV
minimum
value of 11.0592 MHz. With the value FD_VALUE the fractional divider
f
DIV
is adapted to
the module clock frequency
f
ASC
.
defines the deviation of the standard
baudrates when using autobaud detection depending on the module clock
f
ASC
.
Note: If the deviation of the baudrate after autobaud detection is to high, the baudrate
generator (fractional divider FDV and reload register ASCx_BG) can be
reprogrammed if required to get a more precise baudrate with less error.
Table 18-9
Standard Baudrates - Deviations and Errors for Autobaud Detection
f
ASC
FDV
Error in
f
DIV
10 MHz
not possible
12 MHz
472
+0.03%
13 MHz
436
+0.1%
16 MHz
354
+0.03%
18 MHz
315
+0.14%
18.432 MHz
307
-0.07%
20 MHz
283
-0.04%
24 MHz
236
+0.03%
25 MHz
226
-0.22%
30 MHz
189
+0.14%
33 MHz
172
+0.24%
40 MHz
142
+0.31%
Baudrate
f
DIV
d
f
---------
=