Motorola 8900 User Manual - Page 62

A/D Interface 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. Table 2-16: A/D Signals ADC Name Description VCC ADC3 ADC2 ADC1 Power Supply A/D GPAD 3 GPAD 2 GPAD 1 ADC Pin # # Min Max Unit - 5 47 3 43 2 37 1 3.0 4.5 V 0.1 2.5 V 0.1 2.5 V 0.1 2.5 V 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. Table 2-17: GPAD Specifications Parameter Conditions Maximum Operating range Input Voltage Measurement ADC range Voltage Resolution Min Typ Max Unit 0 2.75 V 0.1 2.5 V 10 mV 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. 38 C24 Module Hardware Description December 15, 2008