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:

• 10 microseconds (10uS)
• 100 microseconds (100uS)
• 1 milliseconds (1mS)
• 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:

• Internal - This mode uses the start and stop switches on the front panel of the unit. Each switch has it's own noise filter/de-bounce circuit and the programmable digital noise filter will have no effect on the front panel switches.

• 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)

• 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.

• Run has a two switch external mode as well. The RUN input will start the counter running while the FREEZE input is used to stop the counter (not freeze it). Note that the FREEZE function is NOT available from the remote while using this mode. Selecting the external FREEZE input to be active while using this two switch mode may have undesired effects during operation. It is recommended that FREEZE be set to front panel use. The edge on which each of the inputs triggers is individually programmable. Selecting the RUN or FREEZE input to be non-inverted will make them trigger on the high to low edge. This is also the same as when a switch is first pressed if it is connected to the input. Selecting to invert the input will make the function work on the low to high transition.

• Run can also be used as an external count input. Each time the input is pulsed, the counter will increment by one count. The pulse can be set to trigger on either edge. See Using the Stop Clock as an Event Counter below for more information and user settings.

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:

• Front Panel Mode or External Input select. Selects which source to use. Note that the Filter and Invert setting have no effect when the unit is set for Front Panel mode.

• 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.

• 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.

• The reset line can also be routed to the freeze control (internally) so that it can freeze the display just (20uS) before reset. With an edge triggered reset, this provides a very fast split timing function.

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

• Front Panel mode. The switch on the front panel controls the functionality of the freeze. The counter display is frozen (but the counter keeps counting) as long as the switch is depressed. Releasing the switch will show the current count. The invert and filter settings have no effect when FREEZE is set for front panel operation.

• 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.

• 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).

• 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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