cop87l88rg National Semiconductor Corporation, cop87l88rg Datasheet - Page 20

• Manufacturer Part Number: cop87l88rg
• Description: 8-bit One-time Programmable Microcontroller With Kbytes Program Memory
• Manufacturer: National Semiconductor Corporation

http
Baud Clock Generation
www national com
Prescaler
Select
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
TABLE III Prescaler Factors
NO CLOCK
Prescaler
Factor
1 5
2 5
3 5
4 5
5 5
6 5
7 5
1
2
3
4
5
6
7
8
Prescaler
Select
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110
11111
FIGURE 15 UART BAUD Clock Divisor Registers
(Continued)
FIGURE 14 UART BAUD Clock Generation
Prescaler
Factor
10 5
11 5
12 5
13 5
14 5
15 5
8 5
9 5
10
11
12
13
14
15
16
9
20
As an example considering the Asynchronous Mode and a
CKI clock of 4 608 MHz the prescaler factor selected is
The 2 5 entry is available in Table III The 1 8432 MHz pre-
scaler output is then used with proper Baud Rate Divisor
(Table II) to obtain different baud rates For a baud rate of
19200 e g the entry in Table IV is 5
The divide by 16 is performed because in the asynchronous
mode the input frequency to the UART is 16 times the baud
rate The equation to calculate baud rates is given below
The actual Baud Rate may be found from
N
b
N
1
Baud Rate
e
e
Note The entries in Table IV assume a prescaler
output of 1 8432 MHz In the asynchronous mode
the baud rate could be as high as 625k
5 (N
6 (N is the Baud Rate Divisor)
134 5 (134 58)
110 (110 03)
(1 8432 MHz Prescaler Output)
TABLE IV Baud Rate Divisors
19200
38400
Baud
Rate
b
1200
1800
2400
3600
4800
7200
9600
BR
e
150
300
600
1 is the value from Table IV)
4 608 1 8432
1 8432 MHz (16
e
Fc (16
Divisor
c
Baud Rate
e
N
1046
855
767
383
191
2 5
c
TL DD12860 – 17
95
63
47
31
23
15
11
b
5
2
c
P)
1 (N-1)
6)
e
19200
TL DD12860 – 16