ADUC841 Datasheet, PDF (73/88 Pages) Analog Devices – MicroConverter 12-Bit ADCs and DACs with Embedded High Speed 62-kB Flash MCU

If access to more than 64 kBytes of RAM is desired, a feature
unique to the ADuC841/ADuC842/ADuC843 allows address-
ing up to 16 MBytes of external RAM simply by adding an
additional latch as illustrated in Figure 79.
ADuC841/
ADuC842/
ADuC843 ^P0
ALE
LATCH
SRAM
D0–D7
(DATA)
A0–A7
P2
A8–A15
LATCH
A16–A23
RD
OE
WR
WE
Figure 79. External Data Memory Interface (16 MBytes Address Space)
In either implementation, Port 0 (P0) serves as a multiplexed
address/data bus. It emits the low byte of the data pointer (DPL)
as an address, which is latched by a pulse of ALE prior to data
being placed on the bus by the ADuC841/ADuC842/ADuC843
(write operation) or by the SRAM (read operation). Port 2 (P2)
provides the data pointer page byte (DPP) to be latched by ALE,
followed by the data pointer high byte (DPH). If no latch is
connected to P2, DPP is ignored by the SRAM, and the 8051
standard of 64 kBytes external data memory access is maintained.
Power Supplies
The operational power supply voltage of the parts depends on
whether the part is the 3 V version or the 5 V version. The
specifications are given for power supplies within 2.7 V to 3.6 V
or ±5% of the nominal 5 V level.
Note that Figure 80 and Figure 81 refer to the PQFP package.
For the CSP package, connect the extra DVDD, DGND, AVDD,
and AGND in the same manner. Also, the paddle on the bottom
of the package should be soldered to a metal plate to provide
mechanical stability. This metal plate should not be connected
to ground.
Separate analog and digital power supply pins (AVDD and DVDD,
respectively) allow AVDD to be kept relatively free of the noisy
digital signals that are often present on the system DVDD line.
However, though you can power AVDD and DVDD from two
separate supplies if desired, you must ensure that they remain
within ±0.3 V of one another at all times to avoid damaging the
chip (as per the Absolute Maximum Ratings section). Therefore,
it is recommended that unless AVDD and DVDD are connected
directly together, back-to-back Schottky diodes should be con-
nected between them, as shown in Figure 80.
ADuC841/ADuC842/ADuC843
DIGITAL SUPPLY
10µF
+
–
0.1µF
ANALOG SUPPLY
10µF
+
–
DV_DD
AV_DD
ADuC841/
ADuC842/
ADuC843
DGND
AGND
0.1µF
Figure 80. External Dual-Supply Connections
As an alternative to providing two separate power supplies, the
user can help keep AVDD quiet by placing a small series resistor
and/or ferrite bead between it and DVDD, and then decoupling
AVDD separately to ground. An example of this configuration is
shown in Figure 81. With this configuration, other analog
circuitry (such as op amps and voltage reference) can be powered
from the AVDD supply line as well. The user will still want to
include back-to-back Schottky diodes between AVDD and DVDD
to protect them from power-up and power-down transient
conditions that could momentarily separate the two supply voltages.
DIGITAL SUPPLY
10µF
+
–
0.1µF
BEAD ^1.6Ω
10µF
DV_DD
AV_DD
ADuC841/
ADuC842/
ADuC843
DGND
AGND
0.1µF
Figure 81. External Single-Supply Connections
Notice that in both Figure 80 and Figure 81, a large value
(10 µF) reservoir capacitor sits on DVDD and a separate 10 µF
capacitor sits on AVDD. Also, local small-value (0.1 µF) capaci-
tors are located at each VDD pin of the chip. As per standard
design practice, be sure to include all of these capacitors, and
ensure the smaller capacitors are close to each AVDD pin with
trace lengths as short as possible. Connect the ground terminal
of each of these capacitors directly to the underlying ground
plane. Finally, note that at all times, the analog and digital ground
pins on the part must be referenced to the same system ground
reference point.
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