Measurement Computing USB-4301 - Manual (Page 16)

USB-4301 User's Guide Functional Details
16
Internal frequency values for different base frequencies
1.0000 MHz 1.6667 MHz 3.3333 MHz 5.0000 MHz
FREQ1 1.0000 MHz 1.6667 MHz 3.3333 MHz 5.0000 MHz
FREQ2 100.00 kHz 166.67 kHz 333.33 kHz 500.00 kHz
FREQ3 10.000 kHz 16.667 kHz 33.333 kHz 50.000 kHz
FREQ4 1.0000 kHz 1.6667 kHz 3.3333 kHz 5.0000 kHz
FREQ5 100.00 Hz 166.67 Hz 333.33 Hz 500.00 Hz
External sources
In addition to the five internal sources, the frequency source for the oscillator can be an input signal connected
to any of the five counter input pins ( INP1 – INP5 ) or any of the five gate pins ( GAT1 – GAT5 ). The input signal
can have a maximum frequency of 20 MHz on the counter input pins, and a maximum frequency of 7 MHz on
the gate pins.
The table below applies to all internal and external sources.
Oscillator sources
Source Description
CTRINPUT1 Counter 1 input pin
CTRINPUT2 Counter 2 input pin
CTRINPUT3 Counter 3 input pin
CTRINPUT4 Counter 4 input pin
CTRINPUT5 Counter 5 input pin
GATE1 Counter 1 gate pin
GATE2 Counter 1 gate pin
GATE3 Counter 1 gate pin
GATE4 Counter 1 gate pin
GATE5 Counter 1 gate pin
FREQ1 Internal base frequency
FREQ2 Internal base frequency/10
FREQ3 Internal base frequency/100
FREQ4 Internal base frequency/1000
FREQ5 Internal base frequency/10,000
Divider (OSC divider)
The signal output from the OSC pin is the same frequency as the frequency source divided by a value from 1 to
16. For example, if you select a base frequency of 5.0000 MHz in InstaCal, and choose FREQ3 as the internal
frequency source (50.000 kHz from the Internal frequency values table above), and 8 as the oscillator divider,
the frequency of the signal at the OSC pin is (50.000 kHz / 8) = 6.2500 kHz.
Counter operation
Each of the five counters performs essentially the same function: their internal value either increments or
decrements on each rising or falling edge of their source signal. Since they are all 16-bit counters, they can
count up from 0 to 2 16 -1 = 65,535, or down from 65,535 to 0. When counting up, 65,535 is considered to be the
Terminal Count (TC); when counting down, 0 is the TC. There are a variety of configuration options that can
be used to unlock the power of this basic functionality.