70353C Datasheet, PDF (33/76 Pages) Microchip Technology – Section 21. Enhanced Controller Area Network

Section 21. Enhanced Controller Area Network (ECAN™)
21.5
ECAN OPERATING MODES
The ECAN module can operate in one of the several modes selected by the user application.
These modes include:
• Configuration mode
• Normal Operation mode
• Listen-Only mode
• Listen All Messages mode
• Loopback mode
• Disable mode
The operating modes are requested by the user application that is writing to the Request
Operation Mode bits (REQOP<2:0>) in the ECAN Control Register 1 (CiCTRL1<10:8>). The
ECAN module acknowledges entry into the requested mode by the OPMODE<2:0>
bits (CiCTRL1<7:5>). Mode transition is performed in synchronization with the CAN network.
That is, the ECAN module waits until it detects a bus idle sequence (11 recessive bits) before it
changes mode.
21.5.1 Configuration Mode
After hardware reset, the ECAN module is in the Configuration mode (OPMODE<2:0> = 100).
The error counters are cleared, and all registers contain the Reset values. In order to modify the
ECAN bit time control registers (CiCFG1 and CiCFG2), the ECAN module must be in the
Configuration mode.
21.5.2 Normal Operation Mode
In the Normal Operation mode, the ECAN module can transmit and receive the CAN messages.
Normal Operation mode is requested after initialization by programming the REQOP<2:0>
bits (CiCTRL1<10:8>) to ‘000’. When OPMODE<2:0> = 000, the module proceeds with normal
operation.
21.5.3 Listen-Only Mode
The Listen-Only mode is used mainly for bus monitoring without participating in the transmission
process. The node in Listen-Only mode does not generate an acknowledge or error frames – one
of the other nodes must do it. The Listen-Only mode can be used for detecting the baud rate on
the CAN bus.
21.5.4 Listen All Messages Mode
The Listen All Messages mode is used for system debugging. Basically, all messages are
received, regardless of their identifier, even when there is an error. If the Listen All Messages
mode is activated, the transmission and reception operate the same as Normal Operation mode,
except that if a message is received with an error, it is still transferred to the message buffer.
21.5.5 Loopback Mode
The Loopback mode is used for self-test to allow the ECAN module to receive its own message.
In this mode, the ECAN transmit path is connected to the receive path internally. A “dummy”
acknowledgement is provided, thereby eliminating the need for another node to provide the
Acknowledge bit.
21.5.6 Disable Mode
The Disable mode is used to ensure a safe shutdown before putting the device in Sleep or Idle
mode. That is, the ECAN module waits until it detects a bus idle sequence (11 recessive bits)
before it changes the mode. When the module is in Disable mode, it stops its own clocks, having
no effect on the CPU or other modules. The module wakes up when the bus activity occurs or
when the CPU sets the OPMODE<2:0> bits to ‘000’.
The CiTX pin stays in the recessive state while the module is in Disable mode.
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© 2008-2011 Microchip Technology Inc.
DS70353C-page 21-33