Microchip Technology MA330024 Data Sheet
2009-2014 Microchip Technology Inc.
DS70000591F-page 287
dsPIC33FJ32GS406/606/608/610 and dsPIC33FJ64GS406/606/608/610
21.3
Modes of Operation
The ECAN™ module can operate in one of several
operation modes selected by the user. These modes
include:
operation modes selected by the user. These modes
include:
• Initialization mode
• Disable mode
• Normal Operation mode
• Listen Only mode
• Disable mode
• Normal Operation mode
• Listen Only mode
• Listen All Messages mode
• Loopback mode
Modes are requested by setting the REQOP<2:0> bits
(CxCTRL1<10:8>). Entry into a mode is Acknowledged
by monitoring the OPMODE<2:0> bits (CxCTRL1<7:5>).
The module does not change the mode and the
OPMODE bits until a change in mode is acceptable,
generally during bus Idle time, which is defined as at least
11 consecutive recessive bits.
(CxCTRL1<10:8>). Entry into a mode is Acknowledged
by monitoring the OPMODE<2:0> bits (CxCTRL1<7:5>).
The module does not change the mode and the
OPMODE bits until a change in mode is acceptable,
generally during bus Idle time, which is defined as at least
11 consecutive recessive bits.
21.3.1
INITIALIZATION MODE
In the Initialization mode, the module does not transmit
or receive. The error counters are cleared and the inter-
rupt flags remain unchanged. The user application has
access to Configuration registers that are access
restricted in other modes. The module protects the user
from accidentally violating the CAN protocol through
programming errors. All registers which control the
configuration of the module cannot be modified while
the module is on-line. The ECAN module is not allowed
to enter the Configuration mode while a transmission is
taking place. The Configuration mode serves as a lock
to protect the following registers:
or receive. The error counters are cleared and the inter-
rupt flags remain unchanged. The user application has
access to Configuration registers that are access
restricted in other modes. The module protects the user
from accidentally violating the CAN protocol through
programming errors. All registers which control the
configuration of the module cannot be modified while
the module is on-line. The ECAN module is not allowed
to enter the Configuration mode while a transmission is
taking place. The Configuration mode serves as a lock
to protect the following registers:
• All Module Control Registers
• Baud Rate and Interrupt Configuration Registers
• Bus Timing Registers
• Identifier Acceptance Filter Registers
• Identifier Acceptance Mask Registers
• Baud Rate and Interrupt Configuration Registers
• Bus Timing Registers
• Identifier Acceptance Filter Registers
• Identifier Acceptance Mask Registers
21.3.2
DISABLE MODE
In Disable mode, the module does not transmit or
receive. The module has the ability to set the WAKIF bit
due to bus activity, however, any pending interrupts
remain and the error counters retains their value.
receive. The module has the ability to set the WAKIF bit
due to bus activity, however, any pending interrupts
remain and the error counters retains their value.
If the REQOP<2:0> bits (CxCTRL1<10:8>) = 001, the
module enters the Module Disable mode. If the module
is active, the module waits for 11 recessive bits on the
CAN bus, detects that condition as an Idle bus, then
accepts the module disable command. When the
OPMODE<2:0> bits (CxCTRL1<7:5>) = 001, that
indicates whether the module successfully went into
Module Disable mode. The I/O pins revert to normal
I/O function when the module is in the Module Disable
mode.
module enters the Module Disable mode. If the module
is active, the module waits for 11 recessive bits on the
CAN bus, detects that condition as an Idle bus, then
accepts the module disable command. When the
OPMODE<2:0> bits (CxCTRL1<7:5>) = 001, that
indicates whether the module successfully went into
Module Disable mode. The I/O pins revert to normal
I/O function when the module is in the Module Disable
mode.
The module can be programmed to apply a low-pass
filter function to the CxRX input line while the module or
the CPU is in Sleep mode. The WAKFIL bit
(CxCFG2<14>) enables or disables the filter.
filter function to the CxRX input line while the module or
the CPU is in Sleep mode. The WAKFIL bit
(CxCFG2<14>) enables or disables the filter.
21.3.3
NORMAL OPERATION MODE
Normal Operation mode is selected when
REQOP<2:0> = 000. In this mode, the module is
activated and the I/O pins assume the CAN bus
functions. The module transmits and receives CAN bus
messages via the CxTX and CxRX pins.
REQOP<2:0> = 000. In this mode, the module is
activated and the I/O pins assume the CAN bus
functions. The module transmits and receives CAN bus
messages via the CxTX and CxRX pins.
21.3.4
LISTEN ONLY MODE
If the Listen Only mode is activated, the module on the
CAN bus is passive. The transmitter buffers revert to
the port I/O function. The receive pins remain inputs.
For the receiver, no error flags or Acknowledge signals
are sent. The error counters are deactivated in this
state. The Listen Only mode can be used for detecting
the baud rate on the CAN bus. To use this, it is neces-
sary that there are at least two further nodes that
communicate with each other.
CAN bus is passive. The transmitter buffers revert to
the port I/O function. The receive pins remain inputs.
For the receiver, no error flags or Acknowledge signals
are sent. The error counters are deactivated in this
state. The Listen Only mode can be used for detecting
the baud rate on the CAN bus. To use this, it is neces-
sary that there are at least two further nodes that
communicate with each other.
21.3.5
LISTEN ALL MESSAGES MODE
The module can be set to ignore all errors and receive
any message. The Listen All Messages mode is acti-
vated by setting REQOP<2:0> = 111. In this mode, the
data, which is in the message assembly buffer until the
time an error occurred, is copied in the receive buffer
and can be read via the CPU interface.
any message. The Listen All Messages mode is acti-
vated by setting REQOP<2:0> = 111. In this mode, the
data, which is in the message assembly buffer until the
time an error occurred, is copied in the receive buffer
and can be read via the CPU interface.
21.3.6
LOOPBACK MODE
If the Loopback mode is activated, the module con-
nects the internal transmit signal to the internal receive
signal at the module boundary. The transmit and
receive pins revert to their port I/O function.
nects the internal transmit signal to the internal receive
signal at the module boundary. The transmit and
receive pins revert to their port I/O function.
Note:
Typically, if the ECAN module is allowed to
transmit in a particular mode of operation,
and a transmission is requested immedi-
ately after the ECAN module has been
placed in that mode of operation, the
module waits for 11 consecutive recessive
bits on the bus before starting transmission.
If the user switches to Disable mode within
this 11-bit period, then this transmission is
aborted and the corresponding TXABTmn
bit is set and the TXREQmn bit is cleared.
transmit in a particular mode of operation,
and a transmission is requested immedi-
ately after the ECAN module has been
placed in that mode of operation, the
module waits for 11 consecutive recessive
bits on the bus before starting transmission.
If the user switches to Disable mode within
this 11-bit period, then this transmission is
aborted and the corresponding TXABTmn
bit is set and the TXREQmn bit is cleared.