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Preprocessing

TSC2004

SBAS408E – JUNE 2007 – REVISED MARCH 2008

The TSC2004 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, where limited

bandwidth is a tradeoff, keeping the connection lines to a minimum.

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 these data are all to be

retrieved by host processor for processing, the limited bus bandwidth quickly saturates, along with the host

processor processing capability. In any case, the host processor must always be reserved for more critical tasks,

not for routine work.

The preprocessing unit consists of two main functions: the combined MAV filter (median value filter and

averaging filter), followed by the zone detection.

Preprocessing—Median Value Filter and Averaging Value Filter

The first preprocessing function, a combined MAV filter, can be operated independently as a median value filter

(MVF), an averaging value filter (AVF), and a combined filter (MAVF).

If the acquired signal source is noisy because of the digital switching circuit, it may be necessary to evaluate the

data without noise. In this case, the median value filter (MVF) operation helps to discard the noise. The array of

N converted results is first sorted. 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 = 1, then N = W. A special case is W = 1, which means the MAVF is bypassed. Otherwise, if W > 1, only

averaging is performed on these converted results. In either case, the return value is the averaged value of

window size W of converted results. If M > 1 and W = 1, then N = M, meaning only the median value filter is

operating. The return value is the middle position converted result from the array of M converted results. If M > 1

and W > 1, then N = M. In this case, W < M. The return value is the averaged value of middle portion W of

converted results out of the array of M converted results. Since the value of W is an odd number in this case, the

averaging value is calculated with the middle position converted result counted twice (so a total of W + 1

converted results are averaged).

Table 1. Median Value Filter Size Selection

MEDIAN VALUE FILTER

POSSIBLE AVERAGING WINDOW SIZE

M =

W =

1, 4, 8, 16

1, 3

1, 3, 7

Table 2. Averaging Value Filter Size Selection

AVERAGING VALUE FILTER SIZE SELECTION

W =

M = 1 (Averaging Only)

M > 1

Reserved

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