DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...

For the initial prototype design presented here, the CAN bus arbitration method will be
used to resolve multi-master conflicts on the bus and also provide bidirectional protocol
conversion between CAN and 1 – Wire® devices. For a larger system, having more CAN
nodes and 1 – Wire® devices, other arbitration schemes such as slave-side arbitration would
merit further exploration. This would especially be true for systems where safety-critical and
real-time data throughput is a requirement and also when large amounts of data needs to be
transferred among many CAN nodes and 1 – Wire® devices.
4.3.2 Message IDs vs. Addresses
In bridging two different communication protocols such as CAN and 1 – Wire®, how
to handle converting between message IDs (CAN) and message addresses (1 – Wire®) is a
problem that must be addressed. In a system based upon message IDs, masters broadcast
messages with IDs. All slaves are required to decode the message ID to determine if it is the
intended recipient. For an address-based system, each slave has a unique address, and every
transfer includes the specific address of a slave. Generally, the address is decoded by all slaves
and the intended slave accepts the message and all others reject the message.
One possible way to bridge these two types of systems would be the addition of a simple
PIC® microcontroller to each CAN node. Another way of addressing this problem would be
to use message acceptance filters and masks (typically built-in on CAN Controllers) on each
individual CAN node. A third possible solution would be to use the reserved bits of the
CAN extended identifier field (r0 and r1) as part of an initial address assignment process [40].
86