imported>OCDoc Import: Imported from legacy OpenComputers documentation at ocdoc.cil.li

2026-08-24T08:08:27Z

Imported from legacy OpenComputers documentation at ocdoc.cil.li

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= Component: Modem =

This component is provided by [[Item/network card|network cards]]. Wireless network cards behave much like normal network cards, but additionally send the message as a wireless "packet" when a strength is set. The modem's address must be used for networking. It can be found through component.modem.address.

'''NOTE''': The modem component only works with in-game networks. For out-of-game connections see the [[Item/internet card|internet card]].

Component name: `modem`. Callbacks:

* `isWireless(): boolean`

<pre>Returns whether this modem is capable of sending wireless messages.
</pre>
* `maxPacketSize(): number`

<pre>Returns the maximum packet size for sending messages via network cards. Defaults to 8192. You can change this in the OpenComputers configuration file.
Every value in a message adds two bytes of overhead. (Even if there's only one value.)
Numbers add another 8 bytes, true/false/nil another 4 bytes, and strings exactly as many bytes as the string contains---though empty strings still count as one byte.
Examples:
* `"foo"` is a 5-byte packet; two bytes of overhead and a three byte string.
* `"currentStatus",300` is a 25-byte packet; four bytes overhead, a 13-byte string, and 8 bytes for a number.
</pre>
* `isOpen(port: number): boolean`

<pre>Returns whether the specified "port" is currently being listened on. Messages only trigger signals when they arrive on a port that is open.
</pre>
* `open(port: number): boolean`

<pre>Opens the specified port number for listening. Returns `true` if the port was opened, `false` if it was already open. **Note: maximum port is 65535**
</pre>
* `close([port: number]): boolean`

<pre>Closes the specified port (default: all ports). Returns true if ports were closed.
</pre>
* `send(address: string, port: number[, ...]): boolean`

<pre>Sends a network message to the specified address. Returns `true` if the message was sent. This does ''not'' mean the message was received, only that it was sent. No port-sniffing for you.
Any additional arguments are passed along as data. These arguments must be basic types: nil, boolean, number and string values are supported, tables and functions are not. See [[API/serialization|the serialization API]] for serialization of tables.
The number of additional arguments is limited. The default limit is 8. It can be changed in the OpenComputers configuration file, but this is //not// recommended; higher limits can allow relatively weak computers to break relatively strong ones with no defense possible, while lower limits will prevent some protocols from working.
</pre>
* `broadcast(port: number, ...): boolean`

<pre>Sends a broadcast message. This message is delivered to all reachable network cards. Returns `true` if the message was sent. Note that broadcast messages are ''not'' delivered to the modem that sent the message.
All additional arguments are passed along as data. See `send`.
</pre>
* `getStrength(): number`

<pre>The current signal strength to apply when sending messages.
//Wireless network cards only.//
</pre>
* `setStrength(value: number): number`

<pre>Sets the signal strength. If this is set to a value larger than zero, sending a message will also generate a wireless message. Also, calls to set the strength that exceed the installed modem's maximum strength will simply set the modem's strength to it's maximum. The higher the signal strength the more energy is required to send messages, though.
//Wireless network cards only.//
</pre>
* `getWakeMessage():string`

<pre>Gets the current wake-up message. When the network card detects the wake message (a string in the first argument of a network packet), on any port and the machine is off, the machine is started. Works for robots, cases, servers, drones, and tablets. [[Component/tunnel|Linked Cards]] provide this same functionality.
</pre>
* `setWakeMessage(message: string, [fuzzy: boolean]):string`

<pre>Sets the wake-up message to the specified **string**. The message matching can be fuzzy (default is false). A fuzzy match ignores additional trailing arguments in the network packet.
</pre>
This component generates a signal named `modem_message` if a message from another network card is received.
It has the signature `localAddress: string, remoteAddress: string, port: number, distance: number, ...`.

* `localAddress` is the address of the modem component the message was received by. - `remoteAddress` is the address of the network card the message was sent from. - `port` is the port number the message was delivered to. - `distance` is the distance to the modem that sent the message. This is only set for wireless messages. For normal messages this is always 0. - All further values are values passed along by the sender (i.e. the `...` in `send` and `broadcast`).

== Example use: ```lua local component = require("component") local event = require("event") local m = component.modem -- get primary modem component m.open(123) print(m.isOpen(123)) -- true -- Send some message. m.broadcast(123, "this is a test") -- Wait for a message from another network card. local _, _, from, port, _, message = event.pull("modem_message") print("Got a message from " .. from .. " on port " .. port .. ": " .. tostring(message)) ``` ==

{{:Component/contents}}

Component/modem - Revision history

imported>OCDoc Import: Imported from legacy OpenComputers documentation at ocdoc.cil.li