41081 Chapter 6: Sensing Actuation and Control
Chapter 6 – Input / Output
Sampling of Inputs
• Reading a sensor at a specified period is called sampling.
• The SynchSM period should be chosen to be as large as possible while still safely
satisfying system requirements, in order to reduce microcontroller utilisation.
• Utilisation is the percentage of time that a microcontroller spends executing tasks.
• Lower utilisation translates to a microcontroller consuming less power, supporting
more SynchSM, having less delay from input changes to output changes and having
other desirable features.
• Minimum interevent separation time is the minimum time between any two events
on an input signal.
• The “yh“M’s period should e seleted to e less tha the iiu itereet
separation time, rather than equal, due to allowed tiny variations in tick times in
SynchSM model.
Latency
• The time between the input event and the triggered output event is latency. It is
iportat to redue i order to preet the syste fro eig too slo.
Input Conditioning
• The values sensors provide to a microcontroller commonly must be adjusted to
reduce the impact of imperfections, with such adjustment known as input
conditioning.
• Button debouncing is the task of ignoring the bouncing on a signal from a button, so
that it is interpreted by the system correctly as a single press, and not as multiple
presses.
• A minimum of 50ms sampling period is likely sufficient for most buttons to cover the
period of bouncing.
• Filtering involves ignoring certain input events.
• A systems inputs may be subject to noise, such as electromagnetic interference
(EMI) from nearby electrical products. EMI can cause sensors on sires to output
unintentional 1s (of 0s) for brief periods of time, known as spurious signals, spikes
or glitches.
• A robust solution for this is to require that a 1 be detected for two or more
consecutive samples before being confirmed as a legitimate 1. The same concept can
be applied to a 0.
find more resources at oneclass.com
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Document Summary
Latency: the time between the input event and the triggered output event is latency. It is i(cid:373)porta(cid:374)t to redu(cid:272)e i(cid:374) order to pre(cid:448)e(cid:374)t the syste(cid:373) fro(cid:373) (cid:271)ei(cid:374)g too (cid:862)slo(cid:449)(cid:863). The same concept can be applied to a 0. Avoiding output glitching: a(cid:374) m (cid:272)a(cid:374) a(cid:448)oid output glit(cid:272)hi(cid:374)g (cid:271)y usi(cid:374)g a (cid:448)aria(cid:271)le (cid:862)(cid:272)ou(cid:374)t(cid:863) a(cid:374)d the(cid:374) updati(cid:374)g b all together at the same time rather than consistently changing the value. I/o electrical issues: most digital circuits are designed to easily connect together, however in some cases a direct connection may not work. This is because sometimes a microcontroller output cannot sufficiently drive the device/ devices to which it connects. In a normal set-up , if a pin is not driven with a 0 or 1, (and is thus unconnected), it will yield and indeterminate value, therefore the pin should always be driven.
