SYSTEM CONNECTOR INTERFACE
48
LZT 123 8020 R1A
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.
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
M
Ω
Average supply current
(continuous conversion)
1 mA
External source impedance
50
k
Ω
(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 GM47r5 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 ADCs 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 100k
Ω
pull-up to 2.75V followed by a
series 10k
Ω
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 1M
Ω
minimum. At position 'A' in
Figure 5.12 below, the input characteristics are the same as for
the table above.
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