Down Counter

The Down Counter models a generic down counter with between 2 and 32 output bits.

  • On each clock edge, the D0 ... Dn outputs can decrease one count or hold the last count, depending on the EN pin.
  • The clock-edge trigger can be set with the Trigger Condition parameter to be either rising edge (0_TO_1) or falling edge (1_TO_0).
  • The counter may also be set to a value with the SET pin. When the Set pin goes active, the counter changes to the value specified by the Set To parameter.
  • The Set Type parameter controls whether the set event is asynchronous or synchronous to the CLK edge.

For a counter which counts up, see Up Counter. For a counter that counts up or down, see Up/Down Counter.

In this topic:

Model Name: Down Counter
Simulator: This device is compatible with the SIMPLIS simulator.
Parts Selector Menu Location: Digital Functions > Counters
Symbol Library: None - the symbol is automatically generated when placed or edited.
Model Library: None - the model is automatically generated when the simulation is run.
Subcircuit Names:
  • SIMPLIS_DIGI1_D_DOWN_COUNTER_N : Without Ground Reference
  • SIMPLIS_DIGI1_D_DOWN_COUNTER_Y : With Ground Reference
Symbol:
3-bit, rising edge triggered without ground reference.
Multiple Selections: Only one device at a time can be edited.

Editing the Down Counter

To configure the Down Counter, follow these steps:

  1. Double click the symbol on the schematic to open the editing dialog to the Parameters tab.
  2. Make the appropriate changes to the fields described in the table below the image.
Label Parameter Description
Clock to Output Delay Delay from the triggering clock event until the Counter outputs change
Number of Bits Number of output bits for the Counter
Trigger Condition Determines the triggering condition of the Counter clock pin:
  • 0_TO_1 for rising edge triggered
  • 1_TO_0 for falling edge triggered
Ground Ref Determines whether or not a device has a ground reference pin. Any digital component that has an input or output pin connected to an analog circuit node must have its Ground Ref pin connected to an analog node. This is usually the ground on the schematic.
Minimum Clk Width Minimum valid clock width. Clock widths less than this parameter will not trigger the Counter.
Enable Delay Delay from when the enable pin goes active until the output is enabled
Setup Time Minimum time before the triggering clock event that the input signals must remain steady so that a valid change in each input state is recognized.
Hold Time Minimum time after the triggering clock event that the input signals must remain steady so that a valid change in each input state is recognized.
Initial Condition Initial condition of the Counter output at time=0
Set Delay Delay from when the SET pin goes active until the counter output is reset
Set To Determines the value of the counter output when the SET pin goes active. To set to the maximum count value, assign a value of -1.
Set Level Determines the Set level of counter SET input pin:
  • 1 means active high
  • 0 means active low
Set Type Determines whether or not reset events are synchronized with a clock event
Set Type Description
SYNC Set events are synchronized to the clock edge defined by the Trigger Condition parameter
ASYNC Set events are asynchronous to the clock edge

To define the parameters for the interface between this digital component and each analog component connected directly to an input or output pin, follow these steps:

  1. From the Edit Down Counter dialog box, click on the Interface tab.
  2. Make the appropriate changes to the fields described in the table below the image.
Label Parameter Description
Input Resistance Input resistance of each Counter input pin
Hysteresis, Threshold Hysteresis and Threshold of the inputs. The hysteretic-window width, HYSTWD is centered around Threshold (TH) voltage. To determine the actual threshold ( TL , THI ), substitute Threshold (TH) and Hysteresis (HYSTWD) in each of the following formulas:
Input Logic Level Actual Threshold
1 Threshold + 0.5 * Hysteresis
0 Threshold - 0.5 * Hysteresis
Output Resistance Output resistance of each Counter output pin
Output High Voltage Output high voltage for each Counter output pin
Output Low Voltage Output high voltage for each Counter output pin

Truth Table

The following truth table assumes a Trigger Condition=0_TO_1 which represents a rising edge clocked counter.

Inputs Outputs Action
EN SET CLK D0..Dn
1 0
Count - 1 Count down
0 0
Last count Retain last count
0 1 0 or 1 Set To parameter value Set the counter to the Set To parameter value

Examples

The test circuit used to generate the waveform examples in the next section can be downloaded here: simplis_029_downcounter_example.sxsch.

Waveforms

Subcircuit Parameters

Because the Down Counter model is generated by a template script when the simulation is executed, a hand-coded model cannot be inserted into a netlist. The template script for this device is simplis_make_counter_model.sxscr, which licensed users can download as part of a zip archive of all built-in scripts.

To download the zip archive, follow these steps:

Important: You will be prompted to log in with the user name and password you received with your license file. If you don't have the user name and password, you can email support@simplistechnologies.com with your license information to receive the login credentials. Include a screenshot of the dialog which opens when you run the Help > License Diagnostics... menu.
  1. Click http://www.simetrix.co.uk/simetrix80/scripts.zip to download the script archive.
  2. Enter the user name and password you received with your license file.

The following parameter table defines the parameters used in this model.

Parameter Name Label Data Type Range Units Parameter Description
CLK_TO_OUT_DELAY Clock to Output Delay Number 1f to 1024 s Delay from the triggering clock event until the Counter outputs change
ENABLE_DELAY Enable Delay Number any s Delay from when the enable pin goes active until the output is enabled
GNDREF Ground Ref String
  • 'Y'
  • 'N'
 none Determines whether or not a device has a ground reference pin. Any digital component that has an input or output pin connected to an analog circuit node must have its Ground Ref pin connected to an analog node. This is usually the ground on the schematic.
HOLD_TIME Hold Time Number 1f to 1024 s Minimum time after the triggering clock event that the input signals must remain steady so that a valid change in each input state is recognized.
HYSTWD,
TH		 Hysteresis,
Threshold		 Number min: 1f V Hysteresis and Threshold of the inputs. The hysteretic-window width, HYSTWD is centered around Threshold (TH) voltage. To determine the actual threshold ( TL , THI ), substitute Threshold (TH) and Hysteresis (HYSTWD) in each of the following formulas:
Input Logic Level Actual Threshold
1 Threshold + 0.5 * Hysteresis
0 Threshold - 0.5 * Hysteresis
IC Initial Condition Number
  • 0
  • 1
 none Initial condition of the Counter output at time=0
MIN_CLK Minimum Clk Width Number 1f to 1024 s Minimum valid clock width. Clock widths less than this parameter will not trigger the Counter.
NUMBITS Number of Bits Integer   none Number of output bits for the Counter
RIN Input Resistance Number min: 100 Ω Input resistance of each Counter input pin
ROUT Output Resistance Number min: 1m Ω Output resistance of each Counter output pin
SETUP_TIME Setup Time Number 1f to 1024 s Minimum time before the triggering clock event that the input signals must remain steady so that a valid change in each input state is recognized.
SET_DELAY Set Delay Number any s Delay from when the SET pin goes active until the counter output is reset
SET_LEVEL Set Level Integer
none Determines the Set level of counter SET input pin:
  • 1 means active high
  • 0 means active low
SET_TO Set To Number   none Determines the value of the counter output when the SET pin goes active. To set to the maximum count value, assign a value of -1.
SET_TYPE Set Type String
  • 'ASYNC'
  • 'SYNC'
 none Determines whether or not reset events are synchronized with a clock event
Set Type Description
SYNC Set events are synchronized to the clock edge defined by the Trigger Condition parameter
ASYNC Set events are asynchronous to the clock edge
TRIG_COND Trigger Condition String
  • '0_TO_1'
  • '1_TO_0'
 none Determines the triggering condition of the Counter clock pin:
  • 0_TO_1 for rising edge triggered
  • 1_TO_0 for falling edge triggered
VOH Output High Voltage Number any V Output high voltage for each Counter output pin
VOL Output Low Voltage Number any V Output high voltage for each Counter output pin