Counter (DSP Blockset)

Count up or down through a specified range of numbers.

Library

Switches and Counters, in General DSP

Description

The Counter block increments or decrements an internal counter each time it receives a trigger event at the top input port (Clk). A trigger event at the bottom input port (Rst) resets the counter to its initial state. The triggering event for both inputs is specified by the Count event pop-up menu, and can be one of the following:

Rising edge triggers execution of the block when the trigger input rises from a negative value to zero or a positive value, or from zero to a positive value.
Falling edge triggers execution of the block when the trigger input falls from a positive value to zero or a negative value, or from zero to a negative value.
Either edge triggers execution of the block when either a rising or falling edge (as described above) occurs.
Nonzero sample triggers execution of the block at each sample time that the trigger input is not zero.
Free running disables the trigger (Clk) port and enables the Sample time parameter. The block increments or decrements the counter at a constant interval specified by the Sample time parameter.

At the start of the simulation, the block sets the counter to the value specified by the Initial count parameter, which can be any value in the range defined by the Counter size parameter. The Counter size parameter allows you to choose from three standard counter ranges, or specify an arbitrary counter limit:

8 bits specifies a 256-step (2⁸) counter with a range of 0 to 255.
16 bits specifies a 65536-step (2¹⁶) counter with a range of 0 to 65535.
32 bits specifies a 2³²-step counter with a range of 0 to 2³²-1.
User defined enables the supplementary Maximum count parameter, which allows you to specify an arbitrary upper count limit. The range of the counter is then 0 to the Maximum count value.

When the Count direction parameter is set to Up, a trigger event at the Clk input causes the block to increment the counter by one. The block continues incrementing the counter when triggered until the counter value reaches the upper count limit (e.g., 255 for an 8-bit counter). At the next trigger event, the block resets the counter to 0, and resumes incrementing the counter with the subsequent trigger event.

When the Count direction parameter is set to Down, a trigger event at the Clk input causes the block to decrement the counter by one. The block continues decrementing the counter when triggered until the counter value reaches 0. At the next trigger event, the block resets the counter to the upper count limit (e.g., 255 for an 8-bit counter), and resumes decrementing the counter with the subsequent trigger event.

Between triggering events the block holds the output at its last value. The block resets the counter to its initial state when the trigger event specified in the Count event pop-up menu is received at the optional Rst input. When trigger events are received simultaneously at the Clk and Rst inputs, the block first resets the counter, and then increments or decrements appropriately. If you do not need to reset the counter during the simulation, you can remove the Rst port by deselecting the Reset input check box.

You can change the configuration of output ports on the block icon from the Output pop-up menu. Three options are available:

Count configures the block icon to show a Cnt port, which outputs the current value of the counter.
Hit configures the block icon to show a Hit port. The Hit port outputs zeros while the value of the counter does not equal the Hit value parameter setting. When the counter value does equal the Hit value setting, the block outputs a 1 at the Hits port.
Count and Hit configures the block icon with both ports. This is the default.

All of the counter parameter settings must be integer values, and both inputs must be real.

In the figure below, the Clk input of the Counter block is driven by Simulink's Discrete Pulse Generator block. The Counter block settings are:

Count direction = Down
Count event = Rising edge
Counter size = User defined
Maximum count = 20
Initial count = 5
Output = Count and Hit
Hit value = 4

Frame-Based Operation

When the Frame-based inputs check box is selected, the block interprets each vector input as a frame of data from one channel. Multichannel inputs (i.e., frame matrices) are not accepted.

At each sample time it increments or decrements the counter by the number of trigger events contained in the frame. A trigger event that is split across two consecutive frames is counted in the frame that contains the conclusion of the event. When a trigger event is received at the Rst port, the block first resets the counter, and then increments or decrements the counter by the number of trigger events contained in the frame. The output (the block's count) is still a scalar with the same period as the input.

The Frame-based inputs check box is disabled along with the Clk port in free-running mode.

Dialog Box

Count direction: The counter direction, Up or Down. This parameter is not tunable in Simulink's external mode.
Count event: The type of event that triggers the block to increment/decrement or reset the counter (when received at the Clk or Rst ports, respectively). Free running disables the Clk port, and counts continuously with the period specified by the Sample time parameter.
Sample time: The output sample period in free-running mode.
Counter size: The range of integer values the block should count through before recycling to zero.
Maximum count: The counter's maximum value when Counter size is set to User defined.
Initial count: The counter's initial value at the start of the simulation and after reset. This parameter is not tunable in Simulink's external mode.
Output: Selects the output port(s) to enable: Cnt, Hit, or both.
Hit value: The scalar value whose occurrence in the count should be flagged by a 1 at the (optional) Hit output. This parameter is not tunable in Simulink's external mode.
Reset input: Enable the Rst input port.
Frame-based: Selects frame-based operation.