4E Network

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Revision as of 20:58, 25 February 2006 by Wrchan (Talk) (See Also)

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Introduction

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 full duplex RS485 serial in a star topology. Each device has a dedicated line back to a central node: a Portmaster 2e serial port server.

Wiring

The 4E network requires two twisted pairs. Using the green and orange pairs of CAT 3 or 5 is recommended.

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

Green with white Tx+
White with green Tx-
Orange with white Rx+
White with orange Rx-
Blue with white Left audio
White with blue Audio ground
Brown with white Right audio
White with brown 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,

  • Bemis-6026
  • Walcott-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

where:

  • 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

Addresses

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

  • 0 = unused
  • 1 = server
  • 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'

Ping

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