MC68HC05X4 Datasheet, PDF (100/156 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Motorola CAN
Freescale Semiconductor, Inc.
Single wire
operation
In the event of a bus fault occurring, limited operation of the MCAN bus
may still be possible, depending on the nature of the fault. If the fault is
due to a short circuit between the two bus lines or between one of the
lines and ground, battery voltage or some other potential, it is possible
to identify (using a special software procedure) the line on which the fault
exists and to switch the corresponding comparator input from the faulty
line to the V_DD/2 reference supply. At the same time the driver transistors
to the faulty line should also be switched off. This will allow
communication to continue on the bus. One result of this mode of one
wire transmission is a significant reduction in the common mode range
of the input comparator.
Switching to one wire operation is achieved using the control bits
RX0-passive and RX1-passive in the MCAN command register, located
at address $21. Setting either of these bits will result in the
corresponding input being disconnected from the bus and connected to
V_DD/2.
Sleep mode
If the SLEEP bit in the MCAN command register is set by the processor
the MCAN will go to sleep, unless it is active. If there is activity on the
MCAN bus lines, or there is an interrupt pending, the MCAN is deemed
to be active and will not go to sleep; a wake-up interrupt will be
generated by the MCAN in these circumstances. The SLEEP bit may
also be cleared by the processor, in which case no wake-up interrupt will
be generated. Note that this bit is write-only by the CPU, and it is not
possible therefore to check whether sleep mode has been entered by
reading it. However, the CAF bit in the port configuration register is set
when the MCAN is asleep, and cleared when it is woken up (see Port
configuration register (PCR)).
MC68HC05X4
Motorola CAN
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32-mcan