4E Network
Contents
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 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.
Wiring
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
Now, everything is 6025 and 6026 just listens in.
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
- 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'
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.