ROM

Library:	Memory
Introduced:	2.1.0
Appearance:

Behavior

The ROM component stores up to 16,777,216 values (specified in the Address Bit Width attribute), each of which can include up to to 32 bits (specified in the Data Bit Width attribute). A circuit can access the current values in ROM, but it cannot change them. The user can modify individual values interactively via the Poke Tool, or the user can modify the entire contents via the Menu Tool.

Unlike the RAM component, the ROM component's current contents are stored as an attribute of the component. Thus, if a circuit containing a ROM component is used twice, then both ROM components will hold the same values. Also because of this behavior, the current ROM contents are stored in files created by Logisim.

Current values are displayed in the component. Addresses displayed are listed in gray to the left of the display area. Inside, each value is listed using hexadecimal. The value at the currently selected address will be displayed in inverse text (white on black).

Pins

Adress

Input: Selects which of the values are currently being accessed by the circuit. The bit width is equal to Address Bit Width

Data

Outputs the value at the currently selected address at the Adress pin. The bit width is equal to Data Bit Width

Attributes

When the component is selected or being added, the digits 0 through 9 alter its Address Bit Width attribute and Alt-0 through Alt-9 alter its Data Bit Width attribute.

Address Bit Width

The bit width of the address bits. The number of values stored in ROM is 2^addrBitWidth.

Data Bit Width

The bit width of each individual value in memory.

Contents

Stores the contents of memory.

Poke Tool Behavior

See poking memory in the User's Guide.

Text Tool Behavior

None.

Menu Tool Behavior

See pop-up menus and files in the User's Guide.

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