MC68HC908AS32A Datasheet, PDF (95/280 Pages) Freescale Semiconductor, Inc – Microcontrollers

Low-Power Modes
better understanding of IE.) This results in less of a power saving, but the BDLC is guaranteed to receive
correctly the message which woke it up, since the BDLC internal operating clocks are kept running.
NOTE
Ensuring that all transmissions are complete or aborted before putting the
BDLC into wait mode is important.
4.7.2 Stop Mode
This power-conserving mode is entered automatically from run mode whenever the CPU executes a
STOP instruction or if the CPU executes a WAIT instruction and the WCM bit in the BDLC control
register 1 (BCR1) is previously set. This is the lowest power mode that the BDLC can enter.
A subsequent passive-to-active transition on the J1850 bus will cause the BDLC to wake up and generate
a non-maskable CPU interrupt request. When a STOP instruction is used to put the BDLC in stop mode,
the BDLC is not guaranteed to correctly receive the message which woke it up, since it may take some
time for the BDLC internal operating clocks to restart and stabilize. If a WAIT instruction is used to put the
BDLC in stop mode, the BDLC is guaranteed to correctly receive the byte which woke it up, if and only if
an end-of-frame (EOF) has been detected prior to issuing the WAIT instruction by the CPU. Otherwise,
the BDLC will not correctly receive the byte that woke it up.
If this mode is entered while the BDLC is receiving a message, the first subsequent received edge will
cause the BDLC to wake up immediately, generate a CPU interrupt request, and wait for the BDLC
internal operating clocks to restart and stabilize before normal communications can resume. Therefore,
the BDLC is not guaranteed to receive that message correctly.
NOTE
It is important to ensure all transmissions are complete or aborted prior to
putting the BDLC into stop mode.
MC68HC908AS32A Data Sheet, Rev. 2.0
Freescale Semiconductor
95