User’s Manual
6-35
05.99
On-Chip Peripheral Components
C513AO
6.3.3.1
Using Timer 1 to Generate Baudrates
When Timer 1 is used as the baudrate generator, the baudrates in Modes 1 and 3 are determined
by the timer 1 overflow rate and the value of SMOD as follows:
Modes 1 and 3 baudrate = 2
SMOD
/32
×
(timer 1 overflow rate)
The timer 1 interrupt should be disabled in this application. The timer itself can be configured for
either “timer” or “counter” operation, and in any of its 3 running modes. In the most typical
applications, it is configured for “timer” operation, in the auto-reload mode (high nibble of
TMOD = 0010B). In that case, the baudrate is given by the formula
Modes 1 and 3 baudrate = 2
SMOD
/32
×
f
OSC
/[12
×
(256 – TH1)]
One can achieve very low baudrates with Timer 1 by leaving the Timer 1 interrupt enabled, and
configuring the timer to run as a 16-bit timer (high nibble of TMOD = 0001B), and using the Timer 1
interrupt to do a 16-bit software reload.
Commonly used baudrates, and how they can be obtained from Timer 1, are listed in Table 6-4.
Table 6-4
Timer 1 Generated Commonly Used Baudrates
Baudrate
f
OSC
SMOD
Timer 1
C/T
Mode
Reload
Value
Mode 0 max: 1 MHz
Mode 2 max: 375 K
Modes 1, 3: 62.5 K
19.2 K
9.6 K
4.8 K
2.4 K
1.2 K
110
110
12 MHz
12 MHz
12 MHz
11.059 MHz
11.059 MHz
11.059 MHz
11.059 MHz
11.059 MHz
6 MHz
12 MHz
X
1
1
1
0
0
0
0
0
0
X
X
0
0
0
0
0
0
0
0
X
X
2
2
2
2
2
2
2
1
X
X
FFH
FDH
FDH
FAH
F4H
E8H
72H
FEEBH
