ARCNet is a local area network (LAN). Communication happens by passing a token around a ring of ARCNet nodes. A token is a packet of information sent out on the LAN. Each ARCNet node will examine the token packet. The node will decide whether to accept the packet, and then send the token on to the other nodes in the ring. Communication speeds approaching 2.5 Mbps can be realized. A maximum of 255 nodes make up the LAN. In the PHENIX Muon Tracker, the nodes are configured in a daisy chain fashion.
The Front End Electronics (FEE) for the Muon Tracker has many features that may be configured remotely. Remote configuration of the FEE is necessary because the electronics are located inside of sealed chassis, inside of a sealed magnet, in the beam interaction region which is not accessable during periods of collider operation. ARCNet provides a way to configure the electronics by passing configuration information to the Front End Modules (FEM) over the ARCNet LAN. Each FEM has an ARCNet daughter card that can accept the LAN tokens, and perform the appropriate actions.
There are several functions that ARCNet must perform inside the FEM.
ARCNet must provide the ability to
ARCNet can do all sorts of things, because the Generic ARCNet Board (GAB), developed by Jack Fried, has an 8051 style microcontroller on it. The 8051 I/O ports are used to set up serial data clocking schemes, serial communication with the Dallas chips, and even an embedded JTAG (Joint Test and Action Group) port for EEPROM downloading. Control of the 8051 I/O ports is achieved with C programs, compiled with an 8051 C-compiler, and downloaded in HEX format to the GAB.
Other PHENIX systems are also using ARCNet, so there is a PHENIX ARCNet
Corba server which controls access to the network. If you want to send a
packet over ARCNet, you just give the packet to the Corba server, along with
the node ID of where the packet is supposed to go.
There is also a Java based user interface that will
construct the packets for you, send them out over the LAN, and display any
information that might come back from the FEMs.
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