xAP Configuration, Serial RS485 Bridge and PIC's

["g8kmh" <g8kmh@xxxxxxxxxxx>]

I'm currently in the design stage of my xAP switch assembly. This
would allow 4-8 switches(inputs) to provide either on/off, toggle or
press/hold level. This would allow a wide range of applications, not
least as a humble lightswitch! As an aside, it will be interesting to
see what sort of ramp period and update frequency is required to
allow the message with the level to be sent, mapped, passed across to
the DMX controller and the light level changed - allowing the user to
release at the desired level.

What I'd prefer not to have to do is define, in advance, which port
input is which switch type. With non-PC applications this is going to
come up again and again so what suggestions are there for a generic
implementation?

Finally, as this is going to be a serial connected device (4 wire
RS485) I've noted the xAP serial specification. Has anyone actually
implemented it fully in a PIC? Clearly with limited RAM there are
some restrictions on both tx and rx buffers and the need for the CRC-
16. 'On the fly' parsing/message creation looks the only option.

As to the bridge, I'm going to be using a 4 port card at 38.4kbps so
the general idea is that traffic is broadcast on all ports. The
downside is that the device sending will see the sent message but
this is inevitable since the bridge and the device cannot/shouldn't
care what sort of devices are attached. Traffic buffering will be
needed as well to mux all the messages. Potentially there may be a
need to discard older messages if the ethernet side is flooding the
serial network.

Any comments?

Lehane