UMAX180800, 20 Thermocouple, 2 RTD, 4 Inputs, 6 Relays Dual CAN Controller
Version 1
Page: 19-71
The input states are sampled every 1ms. If debouncing is required, it is set by the
Discrete
Input Debounce Time
configuration parameter. If the
Discrete Input Debounce Time
is zero,
the discrete voltage level input is not debounced.
3.3.4 Frequency and PWM
The frequency and PWM duty cycle measurements are performed by counting high-frequency
internal clock pulses on every period of the input signal. The universal input channels have
different internal organization due to limited hardware resources.
All universal inputs use 16-bit counters with the constant frequency range of 1...10kHz
Table 9. Universal Input Function Block Counters
Function
Block
Counter
Frequency
Range
Counter
Base
Shared Input
Frequency Range
and Debounce Filter
Setting
Universal
Input #1
16-bit
1Hz…10kHz,
Dedicated
N/A
Same input
Universal
Input #2
Dedicated
N/A
Same input
Universal
Input #3
Dedicated
N/A
Same input
Universal
Input #4
Dedicated
N/A
Same input
To measure frequency or PWM duty cycle, the user should first select the
Frequency Range
parameter
and then define how the
Pull-Up/Pull-Down Resistor
,
Frequency/PWM Debounce
Filter
, and the
Frequency/PWM Averaging
parameters should be set.
The
Input Polarity
defines the active edge of the input signal. The
Pull-Up/Pull-Down Resistor
can be used to pull the input to a no-signal state to avoid an undefined input condition when
the signal source is disconnected. The
Input Polarity
and
Pull-Up/Pull-Down Resistor
are
normally set the following way.
Table 10. Setting Pull-Up/Pull-Down Resistor for Selected Input Polarity. Universal Inputs
Input Polarity
Pull-Up/Pull-Down Resistor
Active High
“Disabled” or “10kOhm Pull-Down”
Active Low
“Disabled” or “10kOhm Pull-Up”
The frequency/PWM debounce filter is used to filter out parasitic spikes that can be present in
a noisy input signal. It can be helpful to prevent the input from going into the Recovery state
(see 3.3.4.1 Special Conditions) when, for example, mechanical switches are used to
commutate the input signal.
The debounce filter should be used with caution since it can reduce the accuracy and
resolution of frequency and PWM measurements if the debouncing time is not significantly less
than the period of the input signal.
When a frequency or PWM signal presents a slowly changing parameter, setting an additional
moving average filter using the
Frequency/PWM Averaging
configuration parameter can be
helpful in smoothing the results of the input measurements.
