COP888GW Datasheet, PDF (27/44 Pages) National Semiconductor (TI) – 8-Bit Microcontroller with Pulse Train Generators

Baud Clock Generation (Continued)
As shown in Table V a Prescaler Factor of 0 corresponds to
NO CLOCK This condition is the UART power down mode
where the UART clock is turned off for power saving pur-
pose The user must also turn the UART clock off when a
different baud rate is chosen
The correspondences between the 5-bit Prescaler Select
and Prescaler factors are shown in Table V There are many
ways to calculate the two divisor factors but one particularly
effective method would be to achieve a 1 8432 MHz fre-
quency coming out of the first stage The 1 8432 MHz pre-
scaler output is then used to drive the software programma-
ble baud rate counter to create a 16x clock for the following
baud rates 110 134 5 150 300 600 1200 1800 2400
3600 4800 7200 9600 19200 and 38400 (Table IV) Other
baud rates may be created by using appropriate divisors
The 16x clock is then divided by 16 to provide the rate for
the serial shift registers of the transmitter and receivers
TABLE IV Baud Rate Divisors
(1 8432 MHz PrescaIer Output)
Baud
Rate
Baud Rate
Divisor b 1 (N-1)
110 (110 03)
1046
134 5 (134 58)
855
150
767
300
383
600
191
1200
95
1800
63
2400
47
3600
31
4800
23
7200
15
9600
11
19200
5
38400
2
Note The entries in Table IV assume a prescaIer output of 1 8432 MHz In
asynchronous mode the baud rate could be as high as 625k
TABLE V Prescaler Factors
Prescaler
Select
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110
11111
Prescaler
Factor
NO CLOCK
1
15
2
25
3
35
4
45
5
55
6
65
7
75
8
85
9
95
10
10 5
11
11 5
12
12 5
13
13 5
14
14 5
15
15 5
16
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