ADUC834 Analog Devices, ADUC834 Datasheet - Page 65

• Manufacturer Part Number: ADUC834
• Description: Precision Analog Microcontroller: 1MIPS 8052 MCU + 62kB Flash + 16/24-Bit ADC + 12-Bit DAC
• Manufacturer: Analog Devices

Specifications of ADUC834

• Mcu Core: 8052
• Mcu Speed (mips): 1
• Sram (bytes): 2304Bytes
• Gpio Pins: 34
• Adc # Channels: 4
• Other: PWM

Power Saving Modes
Setting the Idle and Power-Down Mode Bits, PCON.0 and
PCON.1 respectively, in the PCON SFR described in Table II
allows the chip to be switched from Normal mode into Idle
mode, and also into full Power-Down mode.
In Idle mode, the oscillator continues to run, but the core clock
generated from the PLL is halted. The on-chip peripherals
continue to receive the clock and remain functional. The CPU
status is preserved with the stack pointer, program counter, and
all other internal registers maintain their data during Idle mode.
Port pins and DAC output pins also retain their states, and ALE
and PSEN outputs go high in this mode. The chip will recover
from Idle mode upon receiving any enabled interrupt, or on
receiving a hardware reset.
In Power-Down mode, both the PLL and the clock to the core are
stopped. The on-chip oscillator can be halted or can continue to
oscillate, depending on the state of the oscillator power-down
bit (OSC_PD) in the PLLCON SFR. The TIC, being driven
directly from the oscillator, can also be enabled during power-
down. All other on-chip peripherals however, are shut down. Port
pins retain their logic levels in this mode, but the DAC output
goes to a high impedance state (three-state) while ALE and PSEN
outputs are held low. During full Power-Down mode with the
oscillator and wake-up timer running, the ADuC834 typically
consumes a total of 15 A. There are five ways of terminating
Power-Down mode:
Asserting the RESET Pin (Pin 15)
Returns to Normal Mode. All registers are set to their reset
default value and program execution starts at the reset vector
once the RESET pin is deasserted.
Cycling Power
All registers are set to their default state and program execution
starts at the reset vector approximately 128 ms later.
Time Interval Counter (TIC) Interrupt
If the OSC_PD bit in the PLLCON SFR is clear, the 32 kHz
oscillator will remain powered up even in Power-Down mode. If
the Time Interval Counter (Wakeup/RTC timer) is enabled,
a TIC interrupt will wake the ADuC834 up from Power-Down
mode. The CPU services the TIC interrupt. The RETI at the
end of the TIC ISR will return the core to the instruction after
that which enabled power-down.
SPI Interrupt
If the SERIPD Bit in the PCON SFR is set, then an SPI inter-
rupt, if enabled, will wake the ADuC834 up from Power-Down
mode. The CPU services the SPI interrupt. The RETI at the
end of the ISR will return the core to the instruction after that
which enabled power-down.
INT0 Interrupt
If the INT0PD bit in the PCON SFR is set, an external
interrupt 0, if enabled, will wake up the ADuC834 from power-
down. The CPU services the SPI interrupt. The RETI at the end
of the ISR will return the core to the instruction after that which
enabled power-down.
REV. A
–65–
Wake-Up from Power-Down Latency
Even with the 32 kHz crystal enabled during power-down, the
PLL will take some time to lock after a wake-up from power-
down. Typically, the PLL will take about 1 ms to lock. During
this time, code will execute but not at the specified frequency.
Some operations require an accurate clock, for example UART
communications, to achieve specified 50/60 Hz rejection from
the ADCs. The following code may be used to wait for the PLL
to lock:
WAITFORLOCK:
If the crystal has been powered down during power-down, there
is an additional delay associated with the startup of the crystal
oscillator before the PLL can lock. 32 kHz crystals are inherently
slow to oscillate, typically taking about 150 ms. Once again, during
this time before lock, code will execute but the exact frequency
of the clock cannot be guaranteed. Again for any timing sensitive
operations, it is recommended to wait for lock using the lock bit
in PLLCON as shown above.
Grounding and Board Layout Recommendations
As with all high resolution data converters, special attention must
be paid to grounding and PC board layout of ADuC834-based
designs in order to achieve optimum performance from the
ADCs and DAC.
Although the ADuC834 has separate pins for analog and digital
ground (AGND and DGND), the user must not tie these to two
separate ground planes unless the two ground planes are con-
nected together very close to the ADuC834, as illustrated in the
simplified example of Figure 64a. In systems where digital and
analog ground planes are connected together somewhere else
(at the system’s power supply for example), they cannot be
connected again near the ADuC834 since a ground loop would
result. In these cases, tie the ADuC834’s AGND and DGND
Pins all to the analog ground plane, as illustrated in Figure 64b.
In systems with only one ground plane, ensure that the digital
and analog components are physically separated onto separate
halves of the board such that digital return currents do not flow
near analog circuitry and vice versa. The ADuC834 can then be
placed between the digital and analog sections, as illustrated in
Figure 64c.
In all of these scenarios, and in more complicated real-life appli-
cations, keep in mind the flow of current from the supplies and
back to ground. Make sure the return paths for all currents are
as close as possible to the paths the currents took to reach their
destinations. For example, do not power components on the
analog side of Figure 64b with DV
currents from DV
digital currents flowing under analog circuitry, which could happen
if the user placed a noisy digital chip on the left half of the board
in Figure 64c. Whenever possible, avoid large discontinuities in
the ground plane(s) (such as are formed by a long trace on the
same layer), since they force return signals to travel a longer path.
And of course, make all connections to the ground plane directly,
with little or no trace separating the pin from its via to ground.
MOV
JNB
A, PLLCON
ACC.6, WAITFORLOCK
DD
to flow through AGND. Also, try to avoid
DD
since that would force return
ADuC834