User`s guide

15 Frequently Asked Questions

• If the blocks of interest have special ch aracters, retrieve the mangled name

with

tg.showsignals='on' or tg.showpar am = 'on'.

For example, if carriage return

'\n' is part of the block path, the mangled

name returns with carriage returns replaced by spaces.

How Do I Handle Register Rollover for xPC Tar get

Encoder Blocks?

Encoder boards have a fixed size counter register of 16 bits, 24 b its, or 32 bits.

Regardless of th e size, the register always eventually overflow s and r olls over.

This can happen in either the positive or negative direction.

Some boards provide a hardware mech anism to account for overflows or

rollovers. As a best practice, you should design your model to always deal

with overflows or rollovers. An initial count can handle the issue for some

applications.

To handle register rollovers, you can use standard Simulink blocks to design

the following counter algorithm types:

• Rollover Counter — Count the number of rollovers

• Extended Counter — Provide an extended counter that is not limited by

The Incremental Encoder sublibrary of the xPC Target library contains

example blocks for these two ty pes of counters. See Rollover Counter and

Extended Counter for further details. You can use these blocks in your model

as is, or m odified for your model. Connect the output of the encoder block

to these blocks.

These counters perform the following. To view the algorithms used in these

implementations, right-click the subsystem and select the Look Under

Mask option.

• A rollover counter counts the number of tim es the output of an encoder

block has ro lled over. It counts up for positive direction rollovers and down

for negative direction rollovers.

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