Library: Memory
Introduced: 2.3.0


This register holds a single value, whose value is emitted on the output Q. Each time the clock input (diagrammed with a triangle on the component's south edge) triggers according to its Trigger attribute, the value in the register may update based on the two inputs on the component's west edge: The upper input is called load and the lower is called count, and they are interpreted as follows.

loadcounttrigger action
0 or z0 The register remains unchanged.
0 or z1 or z The register increments.
10 The register loads the value found at the D input.
11 or z The register decrements.

The range of the register's counting can be configured using the Maximum Before Reset attribute. When the register reaches this value, the next increment wraps the register back to 0; and if the register is at 0, then a decrement will wrap the register around back to its maximum value.

In addition to the output Q, the component also includes a single-bit output carry. This is 1 whenever the register is at its maximum and the load and count inputs indicate that the component should increment on the next step - or when the register is at 0 and the load and count inputs indicate to decrement at the next step.

The clear input resets the register's value to 0 (all zeroes) asynchronously; that is, as long as the clr input is 1, the value is pinned to 0, regardless of the clock input.


East edge, labeled Q (output, bit width matches Data Bits attribute)
Outputs the value currently stored by the register.
East edge, lower pin (output, bit width 1)
Carry: When load and count indicate to increment, this output is 1 whenever the register is at its maximum. When load and count indicate to decrement, this output is 1 whenever the register is at 0. At all other times, this output is 0.
West edge, top pin (input, bit width 1)
Load: When this is 1 while the count input is 0, the register will load the value found at the data input at the next clock trigger - or, if the count input happens to be 1, the register's value will decrement.
West edge, middle pin labeled D (input, bit with matches Data Bits attribute)
Data: When the clock triggers while load is 1 and count is 0, the register's value changes to the value found at this input.
West edge, lower pin labeled ct (input, bit width 1)
Count: When this is 1 or unconnected, the value in the register increments whenever the clock input is triggered - or it decrements if the load input happens to also be 1.
South edge, indicated with a triangle (input, bit width 1)
Clock: At the instant that this is triggered as specified by the Trigger attribute, the register updates as indicated by the load and count inputs.
South edge, labeled 0 (input, bit width 1)
Clear: When 0 or undefined, this input has no effect. As long as it is 1, the register's value is asynchronously pinned to 0. This occurs asynchronously - that is, without regard to the current clock input value. As long as this is 1, the other inputs have no effect.


Data Bits
The bit width of the value emitted by the component.
Maximum Before Reset
The starting value used for the pseudorandom sequence. If this is 0 (the default), then the starting value is based on the time that the current simulation began.
Configures how the clock input is interpreted. The value rising edge indicates that the register should update its value at the instant when the clock rises from 0 to 1. The falling edge value indicates that it should update at the instant the clock falls from 1 to 0.
The text within the label associated with the component.
Label Font
The font with which to render the label.

Poke Tool Behavior

Clicking the register brings keyboard focus to the register (indicated by a red rectangle), and typing hexadecimal digits will change the value stored in the register.

Text Tool Behavior

Allows the label associated with the component to be edited.

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