81C17 Datasheet, PDF (7/18 Pages) SMSC Corporation – TWENTY PIN UART (TPUART)

THE ON CHIP BAUD RATE GENERATOR
The TPUART incorporates an on chip Baud
Rate Generator that can be programmed to
generate sixteen of the most popular baud rates.
The TPUART also allows the bypassing of the
Baud Rate Generator by programming Mode
Register bit 3 to accept a 16X external clock.
The Baud Rate Generator will not assume any
given baud rate upon power up, therefore it
must be programmed as desired. The following
chart is based on a 5.0688 MHz CLOCK
frequency.
Baud Rate
Select Register
D3 D2 D1 D0
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Baud
Rate
50
110
134.5
150
300
600
1200
1800
2000
2400
3600
4800
7200
9600
19.200
38.400
Table 2 - 16X CLOCK
Clock Frequency = 5.0688 MHz
Theoretical Actual
Frequency Frequency Percent
16X Clock 16X Clock Error
0.8 kHz
1.76
2.152
2.4
4.8
9.6
19.2
28.8
32.0
38.4
57.6
76.8
115.2
153.6
307.2
614.4
0.8 kHz
1.76
2.1523
2.4
4.8
9.6
19.2
28.8
32.081
38.4
57.6
76.8
115.2
153.6
316.8
633.6
0.016
0.253
3.125
3.125
Duty
Cycle %
50/50
50/50
50/50
50/50
50/50
50/50
50/50
50/50
50/50
50/50
50/50
50/50
50/50
48/52
50/50
50/50
Divisor
6336
2880
2356
2112
1056
528
264
176
158
132
88
66
44
33
16
8
7