80C554 Datasheet, PDF (9/76 Pages) NXP Semiconductors – 80C51 8-bit microcontroller . 6 clock operation 16K/512 OTP/ROM/ROMless, 7 channel 10 bit A/D, I2C, PWM, capture/compare, high I/O, 64L LQFP

Philips Semiconductors
80C51 8-bit microcontroller – 6 clock operation
16K/512 OTP/ROM/ROMless, 7 channel 10 bit A/D, I²C, PWM,
capture/compare, high I/O, 64L LQFP
Preliminary specification
80C554/83C554/87C554
OSCILLATOR CHARACTERISTICS
XTAL1 and XTAL2 are the input and output, respectively, of an
inverting amplifier. The pins can be configured for use as an on-chip
oscillator, as shown in the logic symbol.
To drive the device from an external clock source, XTAL1 should be
driven while XTAL2 is left unconnected. The minimum and maximum
high and low times specified in the data sheet must be observed.
V_DD
+
2.2 µF
V_DD
8XC554
RESET
A reset is accomplished by either (1) externally holding the RST pin
high for at least two machine cycles (12 oscillator periods) or (2)
internally by an on-chip power-on detect (POD) circuit which detects
V_CC ramping up from 0 V.
To insure a good external power-on reset, the RST pin must be high
long enough for the oscillator to start up (normally a few
milliseconds) plus two machine cycles. The voltage on V_DD and the
RST pin must come up at the same time for a proper startup.
For a successful internal power-on reset, the V_CC voltage must
ramp up from 0 V smoothly at a ramp rate greater than 5 V/100 ms.
The RST line can also be pulled HIGH internally by a pull-up
transistor activated by the watchdog timer T3. The length of the
output pulse from T3 is 3 machine cycles. A pulse of such short
duration is necessary in order to recover from a processor or system
fault as fast as possible.
Note that the short reset pulse from Timer T3 cannot discharge the
power-on reset capacitor (see Figure 2). Consequently, when the
watchdog timer is also used to set external devices, this capacitor
arrangement should not be connected to the RST pin, and a
different circuit should be used to perform the power-on reset
operation. A timer T3 overflow, if enabled, will force a reset condition
to the 8xC554 by an internal connection, independent of the level of
the RST pin.
A reset may be performed in software by setting the software reset
bit, SRST (AUXR1.5).
V_DD
RST
ON-CHIP
RESISTOR
R_RST
SCHMITT
TRIGGER
OVERFLOW
TIMER T3
RESET
CIRCUITRY
Figure 1. On-Chip Reset Configuration
SU00952
RST
R_RST
SU00953
Figure 2. Power-On Reset
LOW POWER MODES
Stop Clock Mode
The static design enables the clock speed to be reduced down to
0 MHz (stopped). When the oscillator is stopped, the RAM and
Special Function Registers retain their values. This mode allows
step-by-step utilization and permits reduced system power
consumption by lowering the clock frequency down to any value. For
lowest power consumption the Power Down mode is suggested.
Idle Mode
In the idle mode (see Table 2), the CPU puts itself to sleep while
some of the on-chip peripherals stay active. The instruction to
invoke the idle mode is the last instruction executed in the normal
operating mode before the idle mode is activated. The CPU
contents, the on-chip RAM, and all of the special function registers
remain intact during this mode. The idle mode can be terminated
either by any enabled interrupt (at which time the process is picked
up at the interrupt service routine and continued), or by a hardware
reset which starts the processor in the same manner as a power-on
reset.
Power-Down Mode
To save even more power, a Power Down mode (see Table 2) can
be invoked by software. In this mode, the oscillator is stopped and
the instruction that invoked Power Down is the last instruction
executed. The on-chip RAM and Special Function Registers retain
their values down to 2.0 V and care must be taken to return V_CC to
the minimum specified operating voltages before the Power Down
Mode is terminated.
Either a hardware reset or external interrupt can be used to exit from
Power Down. The Wake-up from Power-down bit, WUPD (AUXR1.3)
must be set in order for an external interrupt to cause a wake-up
from power-down. Reset redefines all the SFRs but does not
change the on-chip RAM. An external interrupt allows both the SFRs
and the on-chip RAM to retain their values.
To properly terminate Power Down the reset or external interrupt
should not be executed before V_CC is restored to its normal
operating level and must be held active long enough for the
oscillator to restart and stabilize (normally less than 10 ms).
2000 Nov 10
9