The Xilinx Counter block implements a free-running or count-limited type of an up, down, or up/down counter. The counter output can be specified as a signed or unsigned fixed-point number.
Free-running counters are the least expensive in FPGA hardware.
The free-running up, down, or up/down counter can also be configured to load the
output of the counter with a value on the input
din port by selecting the Provide Load
Pin option in the Block
Parameters dialog box.
The output for a free-running up counter is calculated as follows:
Here N denotes the number of bits in the counter. The free-running down counter calculations replace addition with subtraction.
For the free-running up/down counter, the counter performs addition when input up port is 1 or subtraction when the input up port is 0.
A count-limited counter is implemented by combining a free-running counter with a comparator. Count limited counters are limited to only 64 bits of output precision. Count limited types of a counter can be configured to step between the initial and ending values, provided the step value evenly divides the difference between the initial and ending values.
The output for a count limited up counter is calculated as follows:
The count-limited down counter calculation replaces addition with subtraction. For the count limited up/down counter, the counter performs addition when input up port is 1 or subtraction when input up port is 0.
The output for a free-running up counter with load capability is calculated as follows:
Here N denotes the number of bits in the counter. The down counter calculations replace addition by subtraction.
The Block Parameters dialog box can be invoked by double-clicking the icon in your Simulink model.
- Basic tab
Parameters specific to the Basic tab are as follows:
- Counter type
- Specifies the counter to be a count-limited or free-running counter.
- Count to value
- Sspecifies the ending value, the number at which
the count-limited counter resets. A value of
Infdenotes the largest representable output in the specified precision. This cannot be the same as the initial value.
- Count direction
- Specifies the direction of the count (up or down) or provides an optional input port up (when up/down is selected) for specifying the direction of the counter.
- Initial value
- Specifies the initial value to be the output of the counter.
- Specifies the increment or decrement value.
- Output type
- Specifies the block output to be either Signed or Unsigned.
- Number of bits
- Specifies the number of bits in the block output.
- Binary point
- Specifies the location of the binary point in the block output.
- Provide load port
- When checked, the block operates as a free-running load counter with explicit load and din port. The load capability is available only for the free-running counter.
- Provide Synchronous reset port
- Activates an optional reset (rst) pin on the block. When the reset signal is asserted the block goes back to its initial state. Reset signal has precedence over the optional enable signal available on the block. The reset signal has to run at a multiple of the block's sample rate. The signal driving the reset port must be Boolean.
- Implementation tab
Parameters specific to the Implementation tab are as follows.
- Implementation Details
- Use behavioral HDL (otherwise use core)
- The block is implemented using behavioral HDL. This gives the downstream logic synthesis tool maximum freedom to optimize for performance or area.
- Core Parameters
- Implement using
- Core logic can be implemented in Fabric or in a DSP48, if a DSP48 is available in the target device. The default is Fabric.
Other parameters used by this block are explained in the topic Common Options in Block Parameter Dialog Boxes.
Binary Counter LogiCORE IP Product Guide (PG121)