Difference between revisions of "4E Network"

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*serial port 30-port 6030
*serial port 30-port 6030
Specifically, 6025
==4E Network Protocol==
==4E Network Protocol==

Revision as of 19:03, 24 March 2006


As the number of planned projects increased, it became clear that we needed a set of standards which would allow them to communicate with a central computer and each other. It is not practical to have a separate computer, separate wiring, and a separate communications protocol for every project.

The 4E network uses a combination of half and full duplex RS485 and RS232. Some devices have a dedicated line back to the server while others are on a bus.

The latest version of the 4E network is half duplex RS485 in a bus configuration. The Walcott lounge and bathroom have use this.


The 4E network requires one twisted pairs.

Each bathroom recieves 2 cat 3 cables for Bemix, one for signal and one for power. The signal cable is pinned as shown below

Wire Walcott Bemis
Green with white Tx/Rx+ Tx+
White with green Tx/Rx- Tx-
Orange with white unused Rx+
White with orange unused Rx-
Blue with white Left audio Left audio
White with blue Audio ground Audio ground
Brown with white Right audio Right audio
White with brown Audio ground Audio ground

For the power cable, all colored wires are +12V and all white wires are ground.

Server Hardware

The portmaster serial port server is accessed through telnet:

  • administrative-port 23
  • serial port 0-port 6000
  • serial port 1-port 6001
  • ...
  • serial port 30-port 6030

Specifically, 6025

4E Network Protocol

Packet Format

All data sent over the 4E network is encapsulated in packets. The packet format is outlined below:

  • header code (2 bytes) = escape character + header character
  • header (3 bytes)
  • data (variable length)
  • end code (2 bytes) = escape character + end character


  • escape character = '\'
  • header character = 'H'
  • end character = 'E'

The header contains three 1 byte fields:

  • destination address: This allows the server to route packets from one client to another.
  • source address: This allows one client to respond to a request made by another client.
  • port: This tells the device what type of data to expect and how to processes it.

Note: If the escape character needs to be transmitted in the data block, two should be transmitted instead.

Data and Ports

Currently, only three ports will be implemented:

  • 31 - debug
  • 32 - ping
  • 64 - Bemix

Other possible ports include:

  • EEPROM - for storing data that is currently hardcoded but shouldn't be
  • programming - so the PICs can download their own software
  • cocoa pot
  • other projects


Each device, including the server, is a assigned a unique address.

  • 0 = unused
  • 1 = server
  • 66 (B) = Bemis
  • 67 (C) = control panel
  • 71 (G) = shallow goodale
  • 87 (W) = shallow walcott
  • 92 (\) unused
  • 255 = broadcast, all devices listen

How to control Bemix

When a Bemix client is booted, it sends a packet to the server containing "Bemix v3.0" over the debug port.

Touch Switch Output

The Bemix clients will send an ASCII number 1 through 5, corresponding to the 5 touch switches. The PIC can be programmed to send a single packet when a switch is touched or a continuous stream (at adjustable repeat rate) when it is touched.

Example: touch switches 1 and 5 are touched on device 70 which is programmed to tell device 1 (the server)

'\' 'H' 01 70 64 1 '\' 'E'
'\' 'H' 01 70 64 5 '\' 'E'

Touch Switch Recalibration

The touch switch may be recalibrated by disabling it then reenabling it. This is done by sending a packet containing "D" followed by "E" over the Bemix port:

'\' 'H' 70 01 64 'D' '\' 'E'
'\' 'H' 70 01 64 'E' '\' 'E'


Bemix clients will respond to a packet over the pinging port with an empty packet over the same port.

Example: server pinging device 70 and its response

'\' 'H' 70 01 32 '\' 'E'
'\' 'H' 01 70 32 '\' 'E'

One possible use of pinging is to build a routing table by sending a pinging each serial port to map serial port numbers to device addresses.

To Do

  • Fix bugs with reception
  • Store PIC's address in EEPROM, be able to send an address and data pair and have PIC write it to EEPROM
  • Make devices listen to address 255

PIC Code

See Bemix PIC code.

See Also