TSC2000_08 Datasheet, PDF (31/35 Pages) Texas Instruments – PDA ANALOG INTERFACE CIRCUIT

OPERATION—AUXILIARY MEASUREMENT
The two auxiliary voltage inputs can be measured in much
the same way as the battery inputs, as shown in Figures 24
and 25. Applications might include external temperature
sensing, ambient light monitoring for controlling the back-
light, or sensing the current drawn from the battery.
Host Writes
A/D Converter
Control Register
Start Clock
Power Up Reference
Power Up
A/D Converter
Convert
Auxiliary Input 1
No
Is Data
Averaging Done
Yes
Store Auxiliary Input 1
in AUX1 Register
Auxiliary Input 1
Power Down
A/D Converter
Power Down Reference
Issue Data Available
Turn Off Clock
Done
FIGURE 24. AUX1 Measurement Process.
Host Writes
A/D Converter
Control Register
Start Clock
Power Up Reference
Power Up
A/D Converter
Convert
Auxiliary Input 2
No
Is Data
Averaging Done
Yes
Store Auxiliary Input 2
in AUX2 Register
Auxiliary Input 2
Power Down
A/D Converter
Power Down Reference
Issue Data Available
Turn Off Clock
Done
OPERATION—PORT SCAN
If making measurements of all the analog inputs (except the
touch screen) is desired on a periodic basis, the Port Scan
mode can be used. This mode causes the TSC2000 to
sample and convert both battery inputs and both auxiliary
inputs. At the end of this cycle, the battery and auxiliary result
registers will contain the latest values. Thus, with one write
to the TSC2000, the host can cause four different measure-
ments to be made.
The flowchart for this process is shown in Figure 26. The time
needed to make a complete port scan is given by:
t_READING
= 7.5µs + t_REF+ 4N_AVG

^NBITS
•
1
f_CONV
+ 4.4µs^{}
(8)
Port Scan
Host Writes
A/D Converter
Control Register
Start Clock
Power Up Reference
Power Up
A/D Converter
Convert
Battery Input 1
No
Is Data
Averaging Done
Yes
Store Battery Input 1
in BAT1 Register
Convert
Battery Input 2
No
Is Data
Averaging Done
Yes
Store Battery Input 2
in BAT2 Register
Convert
Auxiliary Input 1
No
Is Data
Averaging Done
Yes
Store Auxiliary Input 1
in AUX1 Register
Convert
Auxiliary Input 2
No
Is Data
Averaging Done
Yes
Store Auxiliary Input 2
in AUX2 Register
Power Down
A/D Converter
Power Down Reference
Issue Data Available
Turn Off Clock
Done
FIGURE 25. AUX2 Measurement Process.
FIGURE 26. Port Scan Mode.
TSC2000
31
SBAS257
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