Datasheet

MSCAN
MC9S12DP256 — Revision 1.1
MSCAN
MSCAN Power
Down Mode
The MSCAN is in Power Down Mode when Table 94
• the CPU is in Stop Mode or
• the CPU is in Wait Mode and the CSWAI bit is set.
When entering the Power Down Mode, the MSCAN immediately stops
all ongoing transmissions and receptions, potentially causing CAN
protocol violations. To protect the CAN bus system from fatal
consequences of violations to the above rule, the MSCAN immediately
drives the TxCAN pin into a recessive state.
CAUTION: The user is responsible for ensuring that the MSCAN is not active when
Power Down Mode is entered. The recommended procedure is to bring
the MSCAN into Sleep Mode before the STOP or WAI instruction (if
CSWAI is set) is executed. Otherwise the abort of an ongoing message
can cause an error condition and can have an impact on the other bus
devices.
In Power Down Mode, all clocks are stopped and no registers can be
accessed. If the MSCAN was not in Sleep Mode before Power Down
Mode became active, the module would perform an internal recovery
cycle after powering up. This causes some fixed delay before the
module enters Run Mode again.
Programmable
Wake-Up Function
The MSCAN can be programmed to wake-up the MSCAN as soon as
bus activity is detected (see control bit WUPE in MSCAN Control 0
Register (CANCTL0)). The sensitivity to existing bus action can be
modified by applying a low-pass filter function to the RxCAN input line
while in Sleep Mode (see control bit WUPM in MSCAN Control 1
Register (CANCTL1)). This feature can be used to protect the MSCAN
from wake-up due to short glitches on the CAN bus lines. Such glitches
can result e.g. from electromagnetic interference within noisy
environments.
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
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