Pin

Library:

Wiring

Introduced:

2.0 Beta 1 (in Base library, moved to Wiring in 2.7.0)

Appearance:

	Arrow		Classic
Pin in:
Pin out:

Behavior

A pin is an output or an input to a circuit, depending on the value of its Type attribute. You can observe above how Logisim represents input and or output pins according to its Appearance attribute.
In the "arrow" mode the inputs will have the connection on the pointed side and the outputs on the rectangular side. In the "classic" appearance the outputs are represented by a circle or rounded rectangle, and the input pins are represented using squares or rectangles.
In all case, the individual bits of the value being sent or received is displayed within the component (except within printer view, when the component only says how many bits wide the pin is).

A pin is a convenient component for interacting with a circuit, and beginning Logisim users need not use them in any other way. But a user building a circuit using several subcircuits (as described in the Subcircuits' section of the section of the User guide will also use pins to specify the interface between a circuit and a subcircuit. In particular, a circuit layout's pin components define the pins that appear on the subcircuit component when the layout is used within another circuit. In such a circuit, the values sent and received to those locations on the subcircuit component are tied to the pins within the subcircuit layout.

Pins

A pin component has only one pin, which will be an input to the component if the pin is an output pin, and it will be an output to the component if the pin is an input pin. In either case, its bit width matches the Data Bits attribute, and its location is specified by the Facing attribute.

Attributes

When the component is selected or being added, Alt-0 through Alt-9 alter its Data Bits attribute. Quick use of the keys allows the entry of larger values for example ALT-1 ALT-2 gives 12. The arrow keys alter its Facing attribute.

Facing: The side of the component where its input/output pin should be.
Type: Specifies whether the component is an Output pin or an Input pin. Note : If the pin component is an input pin, then the pin that acts as its interface within the parent circuit will be an output, and vice versa.
Data Bits: The number of bits for the value that the pin handles.
Behavior: The Behavior attribute is only available for an input pin. The attribute specifies how unknown (floating), U, values should be treated. If the Behavior is Simple or Tri-state, the U values are sent into the layout as U values. Pull Up converts U values to 1 before being sent into the circuit layout. Pull Down converts U values to 0 before being sent into the circuit layout.

The Behavior attribute also specifies what values may be entered into the pin when it is not receiving a value from a parent circuit. Tri-state allows you to enter U values. The other settings do not allow you to enter U values.
Label: The text within the label associated with the component.
Label Font: The font with which to render the label.
Radix: Allows you to define the base in which the values will be represented.
Example for 1010 in binary
Binary : 1010_b
Octal : 12_o
Signed decimal : -6_s
Unsigned decimal : 10_u
Hexadecimal : A_h
Float : 6.0E-07_f if bit width is 16
Float : 1.4E-44_f if bit width is 32
Float : 4.9E-323_f if bit width is 64
Float : NaN_f if bit width is not 16, 32 or 64
Appearance: There are two types of appearance, Classic Logisim and Arrow Shapes. See the examples at the top of the page
Reset Value: An input pin may be given a reset value if it does not have the Tri-state Behavior. The reset value is given as a hexadecimal value. It is loaded into the pin on a simulator reset. If the input pin has Tri-state Behavior, it is loaded with all unknown (floating), U, bits on a reset.

Poke Tool Behavior

Clicking an output pin has no effect, although the pin's attributes will be displayed.

Clicking an input pin will toggle the bit that is clicked. If it is a three-state pin, then the corresponding bit will rotate between the three states.
If the base is Float a small input screen will be displayed.

If, however, the user is viewing the state of a subcircuit as described in the `Debugging Subcircuits' of the User's Guide, then the pin's value is pinned to whatever value the subcircuit is receiving from the containing circuit. The user cannot change the value without breaking this link between the subcircuit's state and the containing circuit's state, and Logisim will prompt the user to verify that breaking this link is actually desired.

Text Tool Behavior

Allows the label associated with the component to be edited.

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