CounterTimer/ShutterControl Module

(20 MHz 232 count Timer and 3 20 MHz 232 count Counters)

  • 20 MHz 232 count (millisecond) Timer and 3 232 count Counters
  • USB-Serial Interface computer control
  • Count in all channels until preset is reached in the selected channel.
  • Input thresholds computer selectable
  • Computer selectable counting edge (rising or falling).
  • Independent front and back panel count inputs.
  • Front panel LEDs show the status of counter channel inputs and control signal output.
  • Output control signal asserted when the C/T-S starts counting and de-asserted when it reaches the preset condition.


The Instrumentation Associates CounterTimer/ShutterControl (CTS) module incorporates a 25 MHz 232 count millisecond timer and 3 232 count counters. The unit is computer controlled through a USB-Serial interface providing flexible instrument configuration for a variety of experimental conditions. It was designed to be employed for the time and/or beam monitor control of X-Ray and neutron diffractometer instruments.

The CTS is equipped with 3 front panel and 3 back panel BNC count inputs and a front panel and back panel BNC control signal output. The thresholds for the count inputs are set from the computer control interface and are retained in non-volatile memory in the device so they do not have to be set following a power down. The front and back panel thresholds are independent and the input to each of the counters is the logical OR of the front and back panel inputs. 

There are several LEDs exposed on the front panel of the CTS that are used to signal the device status.

Power LED.

Green – if Power on

Off – if no power.


Red – if receiving USB communications

Green – if transmitting USB responses

Yellow – if a mix of transmitting and receiving.

Activity LEDs. Located next to the front panel inputs, these LED indicators signal:

  • Green – if counting is enabled and counts are occurring.
  • Off – if counting is enabled and no counts are occurring.
  • Red – if counting is stopped and there is no input activity.
  • Red Flashing - if Paused (Running but Paused) and there is activity at input.
  • Yellow Flashing – if Paused (Running but Paused) and there is not activity at input.
  • Yellow – if counting is stopped but there are threshold crossing at input.

Computer Control

The computer control interface is composed of a few, simple commands that allow the user to:

  • Select the channel that is to be used as the preset channel

  • Specify the preset count or time

  • Specify the analog threshold for the front panel and rear panel input signals

  • Specify the counter signal active edge – rising or falling

  • Specify the polarity of the Shutter Control Signal (active high or active low)

  • Specify the state of the shutter signal (On or Off)

  • Start counting.

  • Pause Counting

  • Resume Counting

  • Stop Counting

  • Query the contents of the counters and timer (these can be read while the counters and timer are active).

Neutron diffraction experiments are normally conducted using a neutron beam monitor to control the duration of the experiment. The IA CounterTimer/ShutterControl (CTS) is designed to provide control of the duration of neutron diffraction experiments either by the preset number of events recorded in a neutron monitor or by a preset time. The CTS is a 1-wide NIM module with three BNC counter inputs and one BNC control signal output. The C/T-S communicates with the host computer via USB bus and appears to the host as a serial port. All of the commands are transmitted as simple single character command codes, some accompanied with data (such as thresholds or preset counts) where appropriate.

Computer Interface/Command Set

Internally the CTS is an FPGA based Counter/Timer module with a USB 2.0 interface. The USB interface goes through a FTDI USART chip to form a serial link between the FTDI chip (USB subsystem) and an Altera AVR processor (ATMEGA329PV -10AU which implements the housekeeping for the module including the DAC interface for setting the thresholds.

After the device driver is installed, the CTS appears as two USB Serial Ports. The first is the interface to the device. The second is an artifact of the (general purpose) driver and is ignored. The serial connection is 8 bits 1 stop bit, no parity and no flow control at 115200 baud. The device can be accessed by a simple terminal emulator (HyperTerm, RealTerm, Ewan …) to experiment with the command set. The commonly used USB interface commands are listed below. There are additional commands, described in the manual, that are used for configuring and querying the device flash memory and the FPGA.


Count Capacity: 232 -1 = 4,294,967,295

Maximum Counting Rate: 25 MHz

Time Base: 50 MHz clock with minimum time interval of 10 ms.

Time Base Accuracy: Within +/- 0.0025% over the 0o-50o C instrument operating range.

Preset Time/Counts: The CTS can be programmed to stop counting when a preselected preset is reached in the selected counter (Counter 1, 2 or 3) or in the timer. Presets can be any value up to the maximum (232-1). If the preset is 0, or presets are disabled, the CTS will run umtil stopped by command of the host computer.

Input discriminators: All of the inputs have computer control discriminators with the discriminator level Vt = 6.4453mV*DAC – 1650mv where DAC is the setting of the (10 bit) DAC associated with the input.

Pulse Pair Resolution: < 20 ns

Input signal levels compatible with ECL, Fast NIM, TTL and CMOS.

Indicators: 6 front panel multicolor LEDs.

Power LED: Green, Power on; Off, no power.

USB LED: Red, receiving USB communications; Green, transmitting USB responses; Yellow – if a mix of transmitting and receiving.

Activity LEDs, located next to the front panel inputs. Green, counting is enabled and counts are occurring; Off, counting is enabled and no counts are occurring, Red, counting is stopped and there is no input activity; Red Flashing, paused (Running but Paused) and there is activity at input; Yellow Flashing, Paused (Running but Paused) and there is no activity at input. Yellow, counting is stopped but there are threshold crossing at input.

Out LED: Green, on, otherwise OFF.