Recently I had a discussion whether one could use RS-485 transceivers for a CAN-bus network in order to gain the flexibility to use the same hardware either in a CAN-environment or in half-duplex RS-485 network, albeit with different software.
The idea is to use a RS-485 bus driver as usual when utilizing the board in RS-485 setup. That this the transmitter is enabled by DEN when one wants to transmit and the bits are presented at the D input as usual. Additional pull-up and pull-downs are provided to ensure valid bus-level upon open bus lines.
When in CAN-Mode, the D input is tied low (dominant) and the DEN input is used to present the bit stream when transmitting. When DEN=1 (driver enabled) the bus is driven low (dominant), otherwise the line remains recessive. This should then mimic the open-collector nature of the CAN bus since only one state is actively driven while the other is only passively pulled by the pull-up resistors.
The driver-enable timings of the SN64HVD11 are given as max. 55ns and the fall time is bounded at 30ns which is less than comparative figures of the "real" CAN driver.
Has someone tried this before? Are there issues I might miss completely?
Clarification: the whole system is intended for a small-scale unmanned vehicle control in the academic domain thus interoperability with 3rd-party components is not deemed important.