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Applies to products: VSC300, VSC400, VT300,
VT400
Overview
The VSC300, VSC400, VT300 and VT400 are a totally new stop clock design based on a new
programmable video generator board developed by MicroImage Video Systems. This new
platform will be used to create several new video products. The stop clock counter core is
totally implemented in hardware. This provides unprecedented speed and accuracy while
removing any high speed counting burden from the main microprocessor. While we were at it,
we made the control section highly programmable to provide maximum interface flexibility.
The models VSC300 and VSC400 Video Stop Clocks can use
their front panel controls to provide many stop clock functions, but the full power of the
units is found when using the remote inputs. The units have 3 external connections on the
remote connector which can be used to control the functionality of the stop clock, either
on their own or in tandem with the front panel.
Front Panel
When using the front panel switches, some of the
functionality is limited compared to what can be accomplished with the external inputs. In
addition, when using the front panel switches, it is recommended to use only two digits of
decimal precision or less (1/100 or 1/10 sec). This is because the front panel switches
have a 1/30 second basic timing which limits precision.
Connections
 Each of the three remote inputs is a logic connection with input
protection. These inputs can be connected to switches (momentary or not), contact
closures, relays or digital logic signals. All inputs have 10K pull-up resistors to the 5V
power supply. The digital logic signals can be driven by TTL or 5V logic levels and in
certain cases, 3.3V logic levels. Any drive input of less than 5V must be able to
withstand the 5V from the 10K pull-up resistor. Some logic is capable of this and some is
not. The external input ground must be at the same potential as the stop
clock unit ground.
The connector used for the remote input is a standard 8 pin mini-din type.
Programmability
Each input can be enabled individually and each input may
have optional digital noise filtering enabled, depending on the noise or switch bounce of
the remote input source. Only one filter time period is selectable for all three inputs.
Each input may also be individually inverted to match the
source input without extra logic or more expensive switches/relays.
The three inputs are named run, reset and freeze.
Under certain circumstances, the run and freeze inputs have alternate functions. We will
cover each input separately.
Digital Noise Filtering
All three inputs of the stop clock feature a digital
noise filter circuit which has a programmable rate. While each input can enable or disable
the filter individually, the rate for all three inputs must be the same. There are four
rate choices (besides turning each input off). The choices are:
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10 microseconds (10uS)
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100 microseconds (100uS)
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1 milliseconds (1mS)
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10 milliseconds (10mS)
The first two rates (10 and 100uS) are primarily for logic
controlled inputs or only slightly noisy inputs.
The second two rates (1mS and 10mS) are designed primarily
to be used with mechanical switches to remove their bounce. Bounce is the phenomenon that
generates a number of rapid contact closures and breaks when the switch is pressed or
disengaged. If these switch bounces are not filtered, they will create an
effect similar
to pressing the switch several times in a row, usually with random results. Please note
that these two rates will reduce the stop/start resolution to 1mS and 10mS intervals
respectively. The 1mS mode can be used with very good quality switches while the 10mS mode
is for garden variety switches. These longer filter rates are most important on the RESET
input when it is set to edge, and on the RUN input when it is set to alternate action. Due
to the nature of these two modes, they are more sensitive to switch bounce (noise) than
that of other selections.
Run
The run input can be set to operate from the front panel or
from the external input. When the front panel is used, there are always separate stop and
start switches. This removes any hazard of accidentally "double pressing" or
"bouncing" the switch and ruining the count. Also, once the start switch is
pressed, any additional press of it has no effect until after the counter is stopped.
Run has several modes when used with the external inputs.
In any of these external modes, the digital noise filter can be applied to the run input.
The digital noise filter will not have any effect when using the front panel controls, as
they have their own preset noise filter.
Following are the different RUN modes which can be selected
through the menu system:
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Run can operate as a gated signal. When the run input is
active, the counter counts. When run is inactive, the counter stops. The polarity of the
run logic is programmable for high or low by selecting to invert or non-invert the RUN
input. With the input set to non-inverted, the RUN input must be a hi logic level or open
connection for the unit to count. If the RUN input is set to inverted, the clock will
count when the input logic level is low (grounded)
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Run can also operate as an alternate action. This is
typically used with a single switch that will stop and start the count. When the RUN input
is pulsed once, the counter starts. Pulsed again, it stops, and so on. The edge on which
it triggers is programmable by changing the INVERT setting for the RUN input. When the
invert setting is set to non-inverted, the counter will stop or start on a high to low
transition, or when a switch connected to the input is first pressed. When set to
inverted, the counter will start or stop on a low to high transition or when an input
connected switch is released.
Reset
Reset can be set to operate from the front panel switch or
from the external remote input. The external inputs also allow a digital filter to clear
the signals or allow the reset input to be inverted. The modes of operation are as
follows:
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The reset input can have edge or logic level control. When
edge controlled, the counter can be reset within 50 microseconds, allowing counting to
continue uninterrupted if needed. The edge can be set to positive or negative by changing
the inverted/non-inverted pin setting. Setting the input to non inverted will allow it to
work when a switch is first pressed, or on the high to low level transition. Setting it to
inverted will use the low to high transition. When logic level controlled, the counter
will remain reset as long as the reset input is active, regardless of whether the counter
is set to run or stop. The active logic level can be set to high or low. Selecting the
input as non-inverted will cause reset to operate as active high (high resets counter, low
allows it to count). This setting can affect the front panel switch as well. In logic
level mode, the counter will remain reset while the switch is depressed. In edge mode, the
counter will reset when the switch is first pressed. In edge mode, the front panel switch
function can not be inverted.
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Reset can have the noise filter enabled or disabled if the
external input is used. If the front panel switch is used, a noise filter/debounce tuned
for the switches is always enabled (see noise filter below). If you are using EDGE mode
with a mechanical switch, a filter of 1mS or 10mS is strongly recommended.
Freeze
The freeze input also has several modes of operation and
the noise filter can be applied to it as needed. Freeze has the following modes. In all
external input modes, the active state of the input pin can be inverted or have the noise
filter applied. Note that external FREEZE functionality will be impaired when the RUN
input is set to Alternate Action. In that case, it is recommended that FREEZE be set to
front panel operation
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External Gate - if the freeze input is active, it freezes
the count displayed on the screen while continuing to count internally. When the signal is
brought inactive, the display resumes at the current count and will continue to be updated
once per frame. Active is defined as a high level when the input is set for non-inverted
and as a low level when set to inverted.
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Freeze/Reset - Freeze can be forced to operate from the
reset input or front panel switch to use split timing. When the reset input is set active
(see RESET above), it will signal the freeze logic to freeze the display just (about
10-20uS) before the counter resets. If the RESET input is set to edge, it will then
continue counting while the display is frozen with the last count. When the RESET switch
is released, or the pin is brought inactive, the display will again show the current
count. In this mode, the external freeze pin is inactive, unless used for the two
switch run mode (see RUN above).
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Last Count on Reset - Freeze can be forced to operate from
the reset input or front panel switch to use another form of split timing. When the reset
input is set active (see RESET above), it will signal the freeze logic to freeze the
display just (about 10-20uS) before the counter resets. If the RESET input is set to
edge, it will then continue counting while the display is frozen with the last
count. When the RESET switch is released, or the pin brought inactive, the display will
remain frozen until the RESET switch is again pressed or the RESET line brought active, at
which time it will show a new (frozen) count. In this mode, the external freeze
pin is inactive, unless used for the two switch run mode (see RUN above).
Using the Stop Clock as an Event
Counter
These units can also be used as a counter instead of a
timer with much of the remote input control flexibility listed above. The run input
becomes the count input and can be used from a switch closure, relay, contact closure or
logic level. This means the unit can easily display a count of people, items on an
assembly line or whatever is required.
In the EVENT COUNTER mode, the counter is set to decade
mode, where each digit rolls over at 9, instead of at 5 in the tens of seconds and tens of
minutes digits as is used with clock counting. This gives a maximum count of 9,999,999,999
before rolling over to 0. When 9,999,999,999 is reached, the counter will return to 0 and
keep counting.
The maximum count rate is one fourth divided by the noise
filter time constant. For example, with a time constant of 10uS, the maximum count rate
would be about 0.25/0.0001 which is about 25Khz. If the filter is set to 10mS, then the
maximum count would be about 25 per second. If the noise filter is turned off, the count
rate can exceed 1Mhz but it will be more noise sensitive.
The FREEZE and RESET inputs work about the same as
explained above and can be used from the front panel or from the external inputs.
Special applications
For applications where none of the above meets the
requirement, please contact MicroImage Video Systems. The core for the stop clock/counter
is highly programmable and it may be possible to update it to meet your needs. Other
modes are also available from the standard core that are only possible by writing specific
driver software for them.
Not only is the stop clock / counter core programmable but
so are most of the other functions such as the video display character generator. As with
the stop clock / counter core, it can be custom adapted to meet unusual or special needs.
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