Horner APG XLt OCS - Manual (Page 39)

MAN0878-04-EN CH. 10
August 12, 2009 Page 39 of 100 ECN # 979
CHAPTER 10: HIGH SPEED I/O (HSC / PWM)
10.1 Overview
In addition to the compliment of simple analog and digital I/O, several of the XLe/XLt I/O modules support
High Speed Counting (HSC) I/O functions and may also support Pulse Width Modulation (PWM) Output
functions. The HSC functions include: frequency, totalizing, pulse width and quadrature measurement.
The PWM functions include: traditional PWM (with variable rate and duty) and a stepper (limited
functionality) with variable acceleration and deceleration rates. To determine function availability, refer to
the associated model’s Specification/Installation sheet (Digital DC Input/Output sections).
This chapter describes the operation of these high level I/O functions. For configuration details of these
functions, see Cscape Configuration (page 71).
10.2
High Speed Counter (HSC) Functions
On units that support the HSC, four dedicated inputs are available than can be configured for one of four
modes of operation. Those modes are Frequency, Count (totalize), Pulse width or period (pulse) and
Quadrature measurement. For some modes, more than one HSC input may be consumed. The
measurement value is provided to ladder in a %AI register (see mapping below).
Note that while the high-speed input circuitry has a resolution of 1 µs, measured
edge transitions must not occur faster than 100 µs for accurate measurements.
Keep in mind that pulse width measurements utilize both the rising and falling
edges of the waveform, thus the pulse width must exist longer than 100 µS.
Note that the edge polarity selection in the mode parameter for the totalize and
pulse width functions (Digital/HSC Input Configuration) assume Positive Logic
regardless of the associated I/O board’s jumper setting for the Digital DC inputs
polarity. If Negative logic is configured when using these functions, the opposite
edge polarity must be selected in the mode parameter.
10.2.1 Frequency
In frequency mode, the frequency of the input signal is written to the accumulator in terms of Hertz
(cycles/second). When using frequency mode, four update selections are provided which specify the
width of the sample window. Note that selecting a shorter sample window provides a quicker
measurement (faster response) but lowers the frequency accuracy (resolution) and increases the
minimum frequency measurement limit.
10.2.2 Totalize
In totalize mode, the accumulator is simply incremented each time the input transitions in a specific
direction. Totalize mode is configurable to specify the edge (rising or falling) on which the accumulator is
incremented.
Rising Edge Signal Falling Edge Signal