If I read this correctly, everything seems easy until the part about
     coexistence on an existing LAN.... Is this a Novell type LAN
     connection?  If so, then the password/timer application will be about
     .1% of the software effort... The rest will be getting your nodes to
     play nice with umpteen other network programs.  Some of which will not
     be perfectly behaved themselves.

     My first thought is to put your time/password application on a PC
     somewhere, and create your own [RS485] LAN segment[s].  The PC can
     easily monitor and control many channels of many nodes each.  That PC
     could have a connection to the Novell LAN if desired.  Now each device
     is needs little more than collision detection or acknowledge/retry to
     get on the network... Network overhead is light enough so that even
     little PICs are appropriate.  There would even be a little horsepower
     left over to check keyboards, and talk to LCD's.

     Joe
     jlittle@mindspring.com



     ------------------------------------------

     Hi everyone,

     I need to design a device that would allow access to a specific
     machine and measures the time the machine was in use.
     This is to be done via a keypad. Every user will have a different
     password. It must be user expandable.

     I think this can be easily done with a PIC. However, the device must
     be able to communicate with a LAN server. All the users passwords, as
     well as time-keeping will be done by the server. The
     device will only "question" the server as of whether the password was
     right or not,
     and if right the server will send an authorization code, the machine
     will activate, and the server will start measuring the time the
     machine
     has been in use. When the user desires to stop using the machine,
     the machine is turned off and the time of use is recorded by the
     server.

     There will be many machines controlled by this device-server
     configuration. Thus, the server must be able to execute parallel
     identification and time keeping.

     So, I guess my question is: Can this be done with PIC's? I have the
     premonition that I need other chip capable of communicating with
     the LAN, which one would that be? Any suggestions or recommendations
     to any of this?

     Regards,

     Pedro