IS80LV52 Datasheet, PDF (22/48 Pages) Integrated Silicon Solution, Inc – CMOS SINGLE CHIP LOW VOLTAGE 8-BIT MICROCONTROLLER

IS80LV52
IS80LV32
ISSI ^®
Using Timer 2 to Generate Baud Rates
In the IS80LV52/32, 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 14.
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.
Modes 1, 3 Baud Rate = ^{Timer 2 Overflow 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 ₌
Oscillator Frequency
Baud Rate
32x [65536 – (RCAP2H, RCAP2L)]
Where (RCAP2H, RCAP2L) is the content of RCAP2H
and RCAP2L taken as a 16-bit unsigned integer.
Figure 13 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
Mode 0 Max: 1 MHz
Mode 2 Max: 375K
Modes 1, 3: 62.5K
19.2K
9.6K
4.8K
2.4K
1.2K
137.5
110
110
fOSC
12 MHz
12 MHz
12 MHz
11.059 MHz
11.059 MHz
11.059 MHz
11.059 MHz
11.059 MHz
11.986 MHz
6 MHz
12 MHz
SMOD
X
1
1
1
0
0
0
0
0
0
0
Timer 1
C/T
Mode
Reload Value
X
X
X
X
X
X
0
2
FFH
0
2
FDH
0
2
FDH
0
2
FAH
0
2
F4H
0
2
E8H
0
2
1DH
0
2
72H
0
1
FEEBH
22
Integrated Silicon Solution, Inc. — 1-800-379-4774
ADVANCE INFORMATION MC019-0A
10/01/98