modem

Modems allow you to send messages between computers over long distances.

Sending and receiving messages

Modems operate on a series of channels, a bit like frequencies on a radio. Any modem can send a message on a particular channel, but only those which have opened the channel and are "listening in" can receive messages.

Channels are represented as an integer between 0 and 65535 inclusive. These channels don't have any defined meaning, though some APIs or programs will assign a meaning to them. For instance, the gps module sends all its messages on channel 65534 (gps.CHANNEL_GPS), while rednet uses channels equal to the computer's ID.

• Sending messages is done with the transmit message.
• Receiving messages is done by listening to the modem_message event.

Types of modem

CC: Tweaked comes with three kinds of modem, with different capabilities.

• Wireless modems: Wireless modems can send messages to any other wireless modem. They can be placed next to a computer, or equipped as a pocket computer or turtle upgrade.

  Wireless modems have a limited range, only sending messages to modems within 64 blocks. This range increases linearly once the modem is above y=96, to a maximum of 384 at world height.

• Ender modems: These are upgraded versions of normal wireless modems. They do not have a distance limit, and can send messages between dimensions.

• Wired modems: These send messages to other any other wired modems connected to the same network (using Networking Cable). They also can be used to attach additional peripherals to a computer.

Recipes

Wireless Modem

Ender Modem

Wired Modem

Networking Cable

6

Wired Modem

Usage

• Wrap a modem and a message on channel 15, requesting a response on channel 43. Then wait for a message to arrive on channel 43 and print it.

  local modem = peripheral.find("modem") or error("No modem attached", 0)
  modem.open(43) -- Open 43 so we can receive replies
  
  -- Send our message
  modem.transmit(15, 43, "Hello, world!")
  
  -- And wait for a reply
  local event, side, channel, replyChannel, message, distance
  repeat
    event, side, channel, replyChannel, message, distance = os.pullEvent("modem_message")
  until channel == 43
  
  print("Received a reply: " .. tostring(message))

See also

• modem_message Queued when a modem receives a message on an open channel.
• rednet A networking API built on top of the modem peripheral.

open(channel)Source

Open a channel on a modem. A channel must be open in order to receive messages. Modems can have up to 128 channels open at one time.

Parameters

1. channel number The channel to open. This must be a number between 0 and 65535.

Throws

• If the channel is out of range.

• If there are too many open channels.

isOpen(channel)Source

Check if a channel is open.

Parameters

1. channel number The channel to check.

Returns

1. boolean Whether the channel is open.

Throws

• If the channel is out of range.

close(channel)Source

Close an open channel, meaning it will no longer receive messages.

Parameters

1. channel number The channel to close.

Throws

• If the channel is out of range.

closeAll()Source

Close all open channels.

transmit(channel, replyChannel, payload)Source

Sends a modem message on a certain channel. Modems listening on the channel will queue a modem_message event on adjacent computers.

🛈 note

The channel does not need be open to send a message.

Parameters

1. channel number The channel to send messages on.
2. replyChannel number The channel that responses to this message should be sent on. This can be the same as channel or entirely different. The channel must have been opened on the sending computer in order to receive the replies.
3. payload any The object to send. This can be any primitive type (boolean, number, string) as well as tables. Other types (like functions), as well as metatables, will not be transmitted.

Throws

• If the channel is out of range.

Usage

• Wrap a modem and a message on channel 15, requesting a response on channel 43.

  local modem = peripheral.find("modem") or error("No modem attached", 0)
  modem.transmit(15, 43, "Hello, world!")

isWireless()Source

Determine if this is a wired or wireless modem.

Some methods (namely those dealing with wired networks and remote peripherals) are only available on wired modems.

Returns

1. boolean true if this is a wireless modem.

getNamesRemote()Source

List all remote peripherals on the wired network.

If this computer is attached to the network, it will not be included in this list.

🛈 note

This function only appears on wired modems. Check isWireless returns false before calling it.

Returns

1. { string... } Remote peripheral names on the network.

isPresentRemote(name)Source

Determine if a peripheral is available on this wired network.

🛈 note

This function only appears on wired modems. Check isWireless returns false before calling it.

Parameters

1. name string The peripheral's name.

Returns

1. boolean boolean If a peripheral is present with the given name.

See also

• peripheral.isPresent

getTypeRemote(name)Source

Get the type of a peripheral is available on this wired network.

🛈 note

This function only appears on wired modems. Check isWireless returns false before calling it.

Parameters

1. name string The peripheral's name.

Returns

1. string | nil The peripheral's type, or nil if it is not present.

See also

• peripheral.getType

Changes

• Changed in version 1.99: Peripherals can have multiple types - this function returns multiple values.

hasTypeRemote(name, type)Source

Check a peripheral is of a particular type.

🛈 note

This function only appears on wired modems. Check isWireless returns false before calling it.

Parameters

1. name string The peripheral's name.
2. type string The type to check.

Returns

1. boolean | nil If a peripheral has a particular type, or nil if it is not present.

See also

• peripheral.getType

Changes

• New in version 1.99

getMethodsRemote(name)Source

Get all available methods for the remote peripheral with the given name.

🛈 note

This function only appears on wired modems. Check isWireless returns false before calling it.

Parameters

1. name string The peripheral's name.

Returns

1. { string... } | nil A list of methods provided by this peripheral, or nil if it is not present.

See also

• peripheral.getMethods

callRemote(remoteName, method, ...)Source

Call a method on a peripheral on this wired network.

🛈 note

This function only appears on wired modems. Check isWireless returns false before calling it.

Parameters

1. remoteName string The name of the peripheral to invoke the method on.
2. method string The name of the method
3. ... Additional arguments to pass to the method

Returns

1. string The return values of the peripheral method.

See also

• peripheral.call

getNameLocal()Source

Returns the network name of the current computer, if the modem is on. This may be used by other computers on the network to wrap this computer as a peripheral.

🛈 note

This function only appears on wired modems. Check isWireless returns false before calling it.

Returns

1. string | nil The current computer's name on the wired network.

Changes

• New in version 1.80pr1.7