參數(shù)資料
型號： P83CL580
廠商： NXP Semiconductors N.V.
英文描述： Low voltage 8-bit microcontrollers with UART, I2C-bus and ADC
中文描述： 低電壓8 - UART的，位微控制器的I2C總線和ADC
文件頁數(shù)： 36/80頁
文件大?。?/td> 366K
代理商： P83CL580
1997 Mar 14
36
Philips Semiconductors
Product specification
Low voltage 8-bit microcontrollers with
UART, I
2
C-bus and ADC
P80CL580; P83CL580
16.3.2
U
SING
T
IMER
2
TO GENERATE BAUD RATES
Timer 2 is selected as a Baud Rate Generator by setting
the RTCLK bit in T2CON. The Baud Rate Generator mode
is similar to the Auto-reload mode, in that a roll-over in TH2
causes Timer 2 registers to be reloaded with the 16-bit
value held in the registers RCAP2H and RCAP2L, which
are preset by software. Baud rates in Modes 1 and 3 are
determined by Timer 2's overflow rate as specified below.
16
The 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). ‘Timer’ operation is slightly
different for Timer 2 when it is being used as a Baud Rate
Generator. Normally, as a timer it would increment every
machine cycle at a frequency of
1
12
×
f
osc
. However, as a
Baud Rate Generator it increments every state time at a
frequency of
1
2
×
f
osc
. In this case the baud rate in
Modes 1 and 3 is determined as:
Baud Rate
Timer 2 Overflow Rate
=
Baud Rate
f
RCAP2H; RCAP2L
32
65536
(
)
–
{
}
×
----------------------------------------------------------------------------------------------------
=
Where (RCAP2H; RCAP2L) is the content of registers
RCAP2H and RCAP2L taken as a 16-bit unsigned integer.
The Baud Rate Generator mode for Timer 2 is shown in
Fig.18. This figure is only valid if RTCLK = 1. At roll-over
TH2 does not set the TF2 bit in T2CON and therefore, will
not generate an interrupt. Consequently, the Timer 2
interrupt does not need to be disabled when in the Baud
Rate Generator mode. If EXEN2 is set, a HIGH-to-LOW
transition on T2EX will set the EXF2 bit, also in T2CON,
but will not cause a reload from (RCAP2H; RCAP2L) to
(TH2, TL2). Therefore, in this mode T2EX may be used as
an additional external interrupt.
When Timer 2 is operating as a timer (TR2 = 1), in the
Baud Rate Generator mode, registers TH2 and TL2 should
not be accessed (read or write). Under these conditions
the timer is being incremented every state time and
therefore the results of a read or write may not be
accurate. The registers RCAP2H and RCAP2L however,
may be read but not written to. A write might overlap a
reload and cause write and/or reload errors. If a write
operation is required, Timer 2 or RCAP2H/RCAP2L
should first be turned off by clearing the TR2 bit.
handbook, full pagewidth
MGD622
TL2
(8 BITS)
TR2
control
TH2
(8 BITS)
RCAP2L
RCAP2H
EXF2
EXEN2
control
C/T2 = 0
C/T2 = 1
T2 PIN
2
OSC
transition
detector
T2EX PIN
TIMER 2 interrupt
(additional external interrupt)
(note: divided by 2
not by 12)
16
RTCLK
RELOAD
CLK
UART receive/
transmit clock
SMOD
1
0
1
0
2
TIMER 1
overflow
Fig.18 Timer 2 in Baud Rate Generator mode.
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