A8351601 Ver la hoja de datos (PDF) - AMIC Technology
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A8351601 Datasheet PDF : 44 Pages
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A8351601 Series
Using Timer 2 to Generate Baud Rates
In the A8351601, setting TCLK and/or RCLK in T2CON
selects Timer 2 as the baud rate generator. Under these
conditions, the baud rates for transmit and receive can be
simultaneously different. Setting RCLK and/or TCLK puts
Timer 2 into its baud rate generator mode, as shown in
Figure 8.
The baud rate generator mode is similar to the auto-reload
mode, in that a rollover in TH2 reloads the Timer 2
registers with the 16-bit value in the RCAP2H and RCAP2L
registers, which are preset by software.
In this case, the baud rates in Mode 1 and 3 are
determined by the Timer 2 overflow rate according to the
following Equation.
Timer 2 Overflow Rate
Modes 1,3 Baud Rate =
16
Timer 2 can be configured for either timer or counter
operation. In the most typical applications, it is configured
for timer operation (C/ T2= 0). Normally, a timer increments
every machine cycle (thus at 1/12 the oscillator frequency),
but timer operation is a different for Timer 2 when it is used
as a baud rate generator. As a baud rate generator, Timer
2 increments every state time (thus at 1/2 the oscillator
frequency). In this case, the baud rate is given by the
following formula.
Modes 1,3
Baud Rate
Oscillator Frequency
=
32 X [65536 - (RCAP2H, RCAP2L)]
Where (RCAP2H, RCAP2L) is the content of RCAP2H and
RCAP2L taken as a 16-bit unsigned integer.
Figure 7 shows Timer 2 as a baud rate generator. This
figure is valid only if RCLK + TCLK = 1 in T2CON. A
rollover in TH2 does not set TF2 and does no generate an
interrupt. Therefore, the Timer 2 interrupt does not have to
be disabled when Timer 2 is in the baud rate generator
mode. If EXEN2 is set, a 1-to-0 transition in T2EX sets
EXF2 but does not cause a reload from (RCAP2H,
RCAP2L) to (TH2, TL2). Thus, when Timer 2 is used as a
baud rate generator, T2EX can be used as an extra
external interrupt.
When Timer 2 is running (TR2 = 1) as a timer in the baud
rate generator mode, programmers should not read from or
write to TH2 or TL2. Under these conditions, Timer 2 is
incremented every state time, and the results of a read or
write may not be accurate. The RCAP registers may be
read, but should not be written to, because a write might
overlap a reload and cause write and/or reload errors. Turn
Timer 2 off (clear TR2) before accessing the Timer 2 or
RCAP registers, in this case.
Table 9. Commonly Used Baud Rates Generated by Timer 1
Baud Rate
fOSC
SMOD
C/ T
Mode 0 Max: 1 MHz
12 MHz
X
X
Mode 2 Max: 375K
12 MHz
1
X
Modes 1,3: 62.5K
12 MHz
1
0
19.2K
11.059 MHz
1
0
9.6K
11.059 MHz
0
0
4.8K
11.059 MHz
0
0
2.4K
11.059 MHz
0
0
1.2K
11.059 MHz
0
0
137.5
11.986 MHz
0
0
110
6 MHz
0
0
110
12 MHz
0
0
Timer 1
Mode
X
X
2
2
2
2
2
2
2
2
1
Reload Value
X
X
FFH
FDH
FDH
FAH
F4H
E8H
1DH
72H
FEEBH
(July, 2002, Version 1.0)
21
AMIC Technology, Inc.
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