参数资料
型号: P89C668HBA
厂商: NXP SEMICONDUCTORS
元件分类: 微控制器/微处理器
英文描述: 80C51 8-bit Flash microcontroller family 64KB ISP FLASH with 8KB RAM
中文描述: 8-BIT, FLASH, 33 MHz, MICROCONTROLLER, PQCC44
封装: PLASTIC, MS-018, SOT-187-2, LCC-44
文件页数: 14/54页
文件大小: 299K
代理商: P89C668HBA
Philips Semiconductors
Preliminary data
P89C668
80C51 8-bit Flash microcontroller family
64KB ISP Flash with 8KB RAM
2001 Jul 27
14
OSC
C/T2 = 0
C/T2 = 1
TR2
Control
TL2
(8-bits)
TH2
(8-bits)
÷
16
RCAP2L
RCAP2H
EXEN2
Control
EXF2
Timer 2
Interrupt
T2EX Pin
Transition
Detector
T2 Pin
Reload
÷
2
“0”
“1”
RX Clock
÷
16
TX Clock
“0”
“1”
“0”
“1”
Timer 1
Overflow
Note availability of additional external interrupt.
SMOD
RCLK
TCLK
SU01213
Figure 6. Timer 2 in Baud Rate Generator Mode
Table 5.
Timer 2 Generated Commonly Used
Baud Rates
Ba d Rate
Baud Rate
Osc Freq
Timer 2
RCAP2H
RCAP2L
750 k
19.2 k
5.6 k
4.8 k
2.4 k
600
220
600
220
12 MHz
12 MHz
12 MHz
12 MHz
12 MHz
12 MHz
12 MHz
6 MHz
6 MHz
FF
FF
FF
FF
FE
FB
F2
FD
F9
FF
D9
B2
64
C8
1E
AF
8F
57
Baud Rate Generator Mode
Bits TCLK and/or RCLK in T2CON (Table 5) allow the serial port
transmit and receive baud rates to be derived from either Timer 1 or
Timer 2. When TCLK= 0, Timer 1 is used as the serial port transmit
baud rate generator. When TCLK= 1, Timer 2 is used as the serial
port transmit baud rate generator. RCLK has the same effect for the
serial port receive baud rate. With these two bits, the serial port can
have different receive and transmit baud rates – one generated by
Timer 1, the other by Timer 2.
Figure 6 shows the Timer 2 in baud rate generation mode. The baud
rate generation mode is like the auto-reload mode,in that a rollover in
TH2 causes the Timer 2 registers to be reloaded with the 16-bit value
in registers RCAP2H and RCAP2L, which are preset by software.
The baud rates in modes 1 and 3 are determined by Timer 2’s
overflow rate given below:
Modes 1 and 3 Baud Rates
Timer 2 Overflow Rate
16
The timer can be configured for either “timer” or “counter” operation.
In many applications, it is configured for “timer” operation (C/T2*=0).
Timer operation is different for Timer 2 when it is being used as a
baud rate generator.
Usually, as a timer it would increment every machine cycle (i.e.,
1
/
6
the oscillator frequency). As a baud rate generator, it increments
at the oscillator frequency. Thus the baud rate formula is as follows:
Oscillator Frequency
[65536
(RCAP2H,RCAP2L)]]
[16
Modes 1 and 3 Baud Rates =
Where:
RCAP2L taken as a 16-bit unsigned integer.
(RCAP2H, RCAP2L)= The content of RCAP2H and
The Timer 2 as a baud rate generator mode shown in Figure 6, is
valid only if RCLK and/or TCLK = 1 in T2CON register. Note that a
rollover in TH2 does not set TF2, and will not generate an interrupt.
Thus, the Timer 2 interrupt does not have to be disabled when
Timer 2 is in the baud rate generator mode. Also if the EXEN2
(T2 external enable flag) is set, a 1-to-0 transition in T2EX
(Timer/counter 2 trigger input) will set EXF2 (T2 external flag) but
will not cause a reload from (RCAP2H, RCAP2L) to (TH2,TL2).
Therefore when Timer 2 is in use as a baud rate generator, T2EX
can be used as an additional external interrupt, if needed.
When Timer 2 is in the baud rate generator mode, one should not try
to read or write TH2 and TL2. As a baud rate generator, Timer 2 is
incremented every state time (osc/2) or asynchronously from pin T2;
under these conditions, a read or write of TH2 or TL2 may not be
accurate. The RCAP2 registers may be read, but should not be
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