The full power of CCNIM (Computer Controlled NIM) is obtainable by adding the RS-232-C option. This plug-in board yields computer control of all functions normally selectable from the front panel, including start and stop count, readout, reset, setting the preset value, displaying the preset value, displaying the counter contents, and selecting the desired time base. To eliminate accidental operator interference, the computer can disable all front-panel controls in the remote mode. Computer readout with the CCNIM option includes the contents of the counter, the preset value, and the current display mode. The CCNIM option can directly drive printers having RS-232-C ports.
Excellent flexibility in setting the preset value is offered by the MN X 10P selection. The M and N values provide two-digit precision, while P selects the decade. Presets can be chosen in the ranges of 0.01 to 990,000 seconds, 0.01 to 990,000 minutes, or 1 to 99,000,000 counts. In the external (EXT) time base mode, the 996 becomes a displayed, preset counter. The 996 can function as a displayed, preset timer by changing the position of a circuit board jumper and using the 0.01-SEC or 0.01-MIN time base.
Both positive and negative sensing inputs to the counter are available on the front panel. The negative input is designed to accept NIM-standard fast negative logic pulses with a fixed threshold of –250 mV on a 50-Ω input impedance. The negative input can handle counting rates up to 100 MHz. The positive input can accept counting rates up to 25 MHz on a 1000-Ω input impedance. To enhance the flexibility of the positive input, a precision discriminator is included. The discriminator threshold is variable over the range of +100 mV to +9.5 V using a front-panel, 25-turn trimpot. The threshold can be adjusted to suit the amplitude of a specific source of logic pulses or used as a precision integral discriminator on analog pulses. For the latter application, the TTL logic output of the discriminator is provided as a test point on the front panel. This output can be used to trigger an oscilloscope while viewing the analog signal at the counter input on the oscilloscope. The oscilloscope trace will show the signals that are being counted by the Model 996, thus permitting a very selective adjustment of the threshold.
All the commonly used functions are conveniently accessible on the front panel. Manual control of the COUNT, STOP, and RESET functions is via three push-buttons. The GATE LED is illuminated when the Model 996 is enabled to count.Selection of the 0.01-s, 0.01-min, or external time base is made by the TIME BASE push button. In the external mode, the preset counter counts the events from the front-panel positive or negative inputs.
The DISPLAY push-button switches the display to show the contents of the counter or the preset stop value. To change the preset value, the preset mode must first be selected with the DISPLAY push button. Subsequently, the PRESET SELECT push button is used to choose M, N, or P for adjustment. Changing the value of M, N, or P is accomplished with the PRESET ADVANCE push button. The display contains LED flags to indicate whether M, N, or P has been selected, to warn when an overflow has occurred in the counter, and to advise when the front-panel controls are disabled by the computer in the remote mode.
When the Model 996 is used without a plug-in option, jumpers on the circuit board can select automatic recycling of the counting interval with a display dwell time of either 1 or 10 s at the end of each counting interval. The plug-in options disable the dwell/automatic recycle function, when enabled by an external controller.
The counting function of the entire module can be disabled by holding the GATE input below +1.5 V using an external signal source. This condition also turns off the GATE LED. Open circuit or greater than +3 V at the GATE input allows the instrument to count, if the COUNT mode has been activated. The INTERVAL output of another ORTEC timer can perform this function to synchronize the Model 996 counting with the other timer. The INTERVAL outputs on all ORTEC timers provide nominally +5 V when counting and less than +0.5 V when counting is inhibited.
The interface connector for the plug-in RS-232-C option is located on the rear panel. The overflow output for the counter is also located on the rear panel. Counting these overflows on another counter effectively extends the counting capacity of the Model 996.
The Model 996 derives its power from the ±12 V, and +6 V supplies in a standard NIM bin with power supply.