User Manual

5. SYSTEM CONNECTOR INTERFACE
47
LZT 123 7589 R1A
5.16.2 Analogue to Digital Converters 1, 2 and 3 - ADCx
The ADC is an 8-bit converter. An analogue value applied to any of the
ADC pins is converted and stored in a register inside the radio device.
When the appropriate AT command is received by the radio device, the
digital value stored in the register is read.
ADC electrical characteristics are shown in the table below.
(9)
Tolerance on this internal voltage is ±5%
5.16.3 Analogue to Digital Converters 4 and 5 - IOx/ADCx
To increase analog input capabilities, the GR47 optimises the I/O by
multiplexing or sharing different features on single pins. There are two
ADC inputs which share system connector pins with digital I/O signals.
When configured as digital I/O, the software will not read the voltages at
the two new ADC inputs. When configured as ADC inputs the software
will configure the digital I/O pins as input or high impedance tri-state. In
this state any applied voltage between 0V and 2.75V can be read as an 8
bit value.
Because the ADC inputs, ADC4 and ADC5, are common with digital I/O,
the input circuit of these Adds is not the same as for the circuits ADC1,
ADC2 and ADC3. It is important to understand the input structure of the
pin so that the correct analog voltage is read by the application (at position
’A’ in Figure 5.12 below). The input structure is provided in Figure 5.12.
It consists of a 100kΩ pull-up to 2.75V followed by a series 10kΩ and 1nF
capacitor to ground which make a low pass filter with a 3dB roll-off at
about 16kHz. The input impedance of the analog IC is 1MΩ minimum.
At position ’A’ in Figure 5.12 below, the input characteristics are the same
as for the table above.
Parameter Min. Max. Units
Resolution 8 8 Bits
Input voltage for 0000 0000 word 0
0.01 x 2.75
(9)
V
Input voltage for 1111 1111 word
0.99 x 2.75
(9)
2.75
(9)
V
Differential Non-Linearity (DNL) ± 0.75 LSB
Overall Non-Linearity (INL) ± 0.60 LSB
Absolute accuracy ± 1.5 LSB
Input impedance 1 MΩ
Average supply current
(continuous conversion)
1mA
External source impedance 50 kΩ