mc68hc912bc32 Freescale Semiconductor, Inc, mc68hc912bc32 Datasheet - Page 216

• Manufacturer Part Number: mc68hc912bc32
• Description: M68hc12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Byte Data Link Communications (BDLC)
To disengage a BDLC node from receiving J1850 traffic:
The BDLC can then be put into wait mode or stop mode and does not wake up with J1850 traffic.
Depending upon which low-power mode instruction the CPU executes and which mode the BDLC enters,
the message which wakes up the BDLC (and the CPU) may not be received correctly. Three possibilities
are described here. These descriptions apply regardless of whether the BDLC is in normal or 4X mode
when the STOP or WAIT instruction is executed.
15.5.1 BDLC Wait and CPU Wait Mode
This power-saving mode is entered automatically from run mode when the WCM bit in BCR1 register is
cleared followed by a CPU WAIT instruction. In BDLC wait mode, the BDLC cannot drive data. A
subsequent J1850 network rising edge wakes up the BDLC.
In this mode, the BDLC internal clocks continue to run as do the MCU clocks. The first passive-to-active
transition on the J1850 network generates a CPU interrupt request by the BDLC which wakes up the
BDLC and CPU. The BDLC correctly receives the entire message which generated the CPU interrupt
request.
15.5.2 BDLC Stop and CPU Wait Mode
This power-conserving mode is entered automatically from run mode when the WCM bit in the BCR1
register is set followed by a CPU WAIT instruction. This is the lowest-power mode that the BDLC can
enter.
In this mode:
The first passive-to-active transition on the J1850 network generates a non-maskable ($20) CPU interrupt
request by the BDLC, allowing the CPU to restart the BDLC internal clocks.
To correctly receive future J1850 wakeup traffic, users must read an EOF (end of frame) in the BSVR
prior to placing the BDLC into stop mode (WCM = 1). Then, the new message which wakes up the BDLC
from the BDLC stop mode and the CPU from the CPU wait mode, is received correctly.
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Verify all BSVR flags are clear.
Do not load the BDR.
Set the ALOOP bit (after placing the analog transceiver into loopback mode) or DLOOP bit in
BCR2.
The BDLC internal clocks are stopped.
The CPU internal clocks continue to run.
The BDLC awaits J1850 network activity.
Ensure that all transmissions are complete or aborted prior to putting the
BDLC into wait mode (WCM = 0 in BCR1).
Ensure that all transmissions are complete or aborted prior to putting the
BDLC into stop mode (WCM = 1 in BCR1).
M68HC12B Family Data Sheet, Rev. 9.1
NOTE
NOTE
Freescale Semiconductor