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A/D Interface
38 C24 Module Hardware Description December 15, 2008
A/D Interface
The C24 includes 4 Analog to Digital Converter (ADC) signals with 8-bit resolution, for
environmental and electrical measurements. The ADC signals measure an analog DC voltage
level on their inputs which is converted to an 8-bit digital value for further processing by C24 or
the user application.
The A/D signals operation and reporting mechanism is defined by the AT+MMAD command.
Table 2-16 below, lists the internal and external A/D signals provided by C24.
General Purpose A/D
The C24 provides 3 general purpose A/D (GPAD) signals for customer application use. Each A/D
signal can monitor a separate external voltage and report its measured level independently to the
application, through the AT command interface.
The GPAD signals measure a DC voltage level of 0.1 - 2.5 V, which is converted internally to a
8-bit digital value. The user application can monitor the A/D voltage level through the
AT+MMAD command, which returns the measured DC level in Volts times 100.
For example, a measured analog DC level of 1.75 Volts will be presented as 175 by the MMAD
command.
Table 2-17 gives the GPAD specifications.
Power Supply A/D
The main power supply (VCC) is constantly monitored internally by the C24 through a dedicated
A/D signal, which is not accessible on the interface connector.
Table 2-16: A/D Signals
ADC Name Description Pin #
ADC
# Min Max Unit
VCC Power Supply A/D - 5 3.0 4.5 V
ADC3 GPAD 3 47 3 0.1 2.5 V
ADC2 GPAD 2 43 2 0.1 2.5 V
ADC1 GPAD 1 37 1 0.1 2.5 V
Table 2-17: GPAD Specifications
Parameter Conditions Min Typ Max Unit
Maximum
Input Voltage Operating range 0 2.75 V
Measurement
Voltage ADC range 0.1 2.5 V
Resolution 10 mV