TSC2013-Q1 Datasheet, PDF (21/70 Pages) Texas Instruments – TSC2013-Q1 12-Bit, Nanopower, 4-Wire Dual-Touch Screen Controller With I2C Interface

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TSC2013-Q1
SLVSC89A – JUNE 2014 – REVISED JULY 2014
Feature Description (continued)
In modes where the TSC2013-Q1 device must detect whether or not a touch remains on the screen (for
example, when doing a pen-touch-initiated X, Y, and Z conversion), the TSC2013-Q1 device must reset the
drivers to connect the R_(IRQ) resistor again. Because of the high value of this pullup resistor, any capacitance on
the touch screen inputs causes a long delay time, and may prevent the detection from occurring correctly. To
prevent this possible delay, the TSC2013-Q1 device has a circuit that allows prechargingd any screen
capacitance, so that the pullup resistor must not be the only source for the charging current. The setting for the
time allowed for this precharge, as well as the time needed to sense if the screen touch remains, is in the
configuration register.
This configuration underscores the need to use the minimum possible capacitor values on the touch-screen
inputs. Capacitors can be used to reduce noise, but capacitors with too large a value increase the required
precharge and sense times, as well as the panel voltage-stabilization time.
7.3.3.6 Preprocessing
The TSC2013-Q1 device offers an array of powerful preprocessing operations that reduce unnecessary traffic on
the bus and reduce the host processor loading. This reduction is especially critical for the serial interface
because of the slow bus speed and the high CPU bandwidth required for I²C communication.
All data-acquisition tasks are looking for specific data that meet certain criteria. Many of these tasks fall into a
predefined range, while other tasks may be looking for a value in a noisy environment. If the host processor is to
retrieve all these data for processing, the limited bus bandwidth quickly saturates, along with the host processor
processing capability. In any case, reserving the host processor for more critical tasks rather than routine work is
always necessary.
The preprocessing unit consists of two main functions which result in the combined MAV (median and averaging-
value) filter: the median value filter (MVF) and the averaging-value filter (AVF).
7.3.3.6.1 Preprocessing—Median Value Filter and Averaging Value Filter
The first preprocessing function, a combined MAV filter, can operate independently as a median value filter
(MVF), an averaging value filter (AVF), and a combined filter (MAV filter).
If the acquired signal source is noisy because of the digital switching circuit, evaluating the data without noise
may be necessary. In this case, the median value filter (MVF) operation helps to discard noise. The first action is
sorting the array of N converted results. The return value is either the middle (median value) of an array of M
converted results, or the average value of a window size of W of converted results:
N
= the total number of converted results used by the MAV filter
M
= the median value filter size programmed
W
= the averaging window size programmed
If M is equal to 1, then N is equal to W. A special case is W equal to 1, which indicates a bypassed MAV filter.
Otherwise, if W is greater than 1, averaging is the only function performed on these converted results. In either
case, the return value is the averaged value of window size W of converted results.
If M is greater than 1 and W is equal to 1, then N is equal to M, meaning the only operating filter is the median
value filter. The return value is the middle position converted result from the array of M converted results.
If M is greater than 1 and W is greater than 1, then N is equal to M. In this case, W is less than M. The return
value is the averaged value of middle portion W of converted results out of the array of M converted results.
Because the value of W is an odd number in this case, the calculation of the averaging value counts the middle-
position converted result twice (averaging a total of W + 1 converted results).
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