ADUC847BCP8-5 AD [Analog Devices], ADUC847BCP8-5 Datasheet - Page 92

• Manufacturer Part Number: ADUC847BCP8-5
• Description: MicroConverter Multichannel 24-/16-Bit ADCs with Embedded 62 kB Flash and Single-Cycle MCU
• Manufacturer: AD [Analog Devices]

ADuC845/ADuC847/ADuC848
Single-Pin Emulation Mode
Built into the ADuC845/ADuC847/ADuC848 is a dedicated
controller for single-pin in-circuit emulation (ICE). In this mode,
emulation access is gained by connection to a single pin, the EA
pin. Normally on the 8051 standard, this pin is hardwired either
high or low to select execution from internal or external program
memory space. Note that external program memory or execu-
tion from external program memory is not allowed on the
devices. To enable single-pin emulation mode, users need to pull
the EA pin high through a 1 kΩ resistor as shown in Figure 69.
The emulator then connects to the 2-pin header also shown in
Figure 69. To be compatible with the standard connector that
comes with the single-pin emulator available from Accutron
Limited (www.accutron.com), use a 2-pin 0.1-inch pitch
Friction Lock header from Molex (www.molex.com) such as
part number 22-27-2021. Be sure to observe the polarity of this
header. As shown in Figure 69, when the Friction Lock tab is at
the right, the ground pin should be the lower of the two pins
when viewed from the top.
Typical System Configuration
A typical ADuC845/ADuC847/ADuC848 configuration is
shown in Figure 69. Figure 69 also includes connections for a
typical analog measurement application of the parts, namely an
interface to an resistive temperature device (RTD). The
arrangement shown is commonly referred to as a 4-wire RTD
configuration.
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Here, the on-chip excitation current sources are enabled to
excite the sensor. The excitation current flows directly through
the RTD generating a voltage across the RTD proportional to its
resistance. This differential voltage is routed directly to one set
of the positive and negative inputs of the ADC (AIN1, AIN2,
respectively in this case). The same current that excited the
RTD also flows through a series resistance, R
ratiometric voltage reference, V
reference ensures that variations in the excitation current do not
affect the measurement system since the input voltage from the
RTD and reference voltage across R
the excitation current. Resistor R
temperature coefficient to avoid errors in the reference voltage
overtemperature. R
least a 1 V voltage reference.
The preceding example shows just a single differential ADC
connection using a single reference input pair. The ADuC845/
ADuC847/ADuC848 have the capability of connecting to five
differential inputs directly or ten single-ended inputs (LFCSP
package only) as well as having a second reference input. This
arrangement means that different sensors with different
reference ranges can be connected to the part with the need for
external multiplexing circuitry. This arrangement is shown in
Figure 70. The bridge sensor shown can be a load cell or a
pressure sensor. The RTD is shown using a reference voltage
derived from the R
bridge sensor is shown using a divided down AV
the REFIN2± inputs.
REF
REF
resistor via the REFIN± inputs, and the
must also be large enough to generate at
REF
REF
. The ratiometric voltage
REF
must, however, have a low
vary ratiometrically with
REF
, generating a
DD
reference via