PIC18F2680ISPQTP datasheet(327/482 Pages) MICROCHIP

327 / 482 page

Preliminary

DS39625C-page 325

PIC18F2585/2680/4585/4680

23.3.4

LISTEN ONLY MODE

Listen

Only

mode

provides

means

for

the

PIC18F2585/2680/4585/4680 devices to receive all

messages, including messages with errors. This mode

can be used for bus monitor applications or for

detecting the baud rate in ‘hot plugging’ situations. For

Auto-Baud Detection, it is necessary that there are at

least two other nodes which are communicating with

each other. The baud rate can be detected empirically

by testing different values until valid messages are

received. The Listen Only mode is a silent mode,

meaning no messages will be transmitted while in this

state, including error flags or Acknowledge signals. The

filters and masks can be used to allow only particular

messages to be loaded into the receive registers or the

filter masks can be set to all zeros to allow a message

with any identifier to pass. The error counters are reset

and deactivated in this state. The Listen Only mode is

activated by setting the mode request bits in the

CANCON register.

23.3.5

LOOPBACK MODE

This mode will allow internal transmission of messages

from the transmit buffers to the receive buffers without

actually transmitting messages on the CAN bus. This

mode can be used in system development and testing.

In this mode, the ACK bit is ignored and the device will

allow incoming messages from itself, just as if they

were coming from another node. The Loopback mode

is a silent mode, meaning no messages will be

transmitted while in this state, including error flags or

Acknowledge signals. The TXCAN pin will revert to port

I/O while the device is in this mode. The filters and

masks can be used to allow only particular messages

to be loaded into the receive registers. The masks can

be set to all zeros to provide a mode that accepts all

messages. The Loopback mode is activated by setting

the mode request bits in the CANCON register.

23.3.6

ERROR RECOGNITION MODE

The module can be set to ignore all errors and receive

any message. In functional Mode 0, the Error Recogni-

tion mode is activated by setting the RXM<1:0> bits in

the RXBnCON registers to ‘11’. In this mode, the data

which is in the message assembly buffer until the error

time, is copied in the receive buffer and can be read via

the CPU interface.

23.4

ECAN Module Functional Modes

In addition to CAN modes of operation, the ECAN mod-

ule offers a total of 3 functional modes. Each of these

modes are identified as Mode 0, Mode 1 and Mode 2.

23.4.1

MODE 0 – LEGACY MODE

Mode 0 is designed to be fully compatible with CAN

modules used in PIC18CXX8 and PIC18FXX8 devices.

This is the default mode of operation on all Reset

conditions. As a result, module code written for the

PIC18XX8 CAN module may be used on the ECAN

module without any code changes.

The following is the list of resources available in Mode 0:

• Three transmit buffers: TXB0, TXB1 and TXB2

• Two receive buffers: RXB0 and RXB1

• Two acceptance masks, one for each receive

buffer: RXM0, RXM1

• Six acceptance filters, 2 for RXB0 and 4 for RXB1:

RXF0, RXF1, RXF2, RXF3, RXF4, RXF5

23.4.2

MODE 1 – ENHANCED

LEGACY MODE

Mode 1 is similar to Mode 0, with the exception that

more resources are available in Mode 1. There are 16

acceptance filters and two acceptance mask registers.

Acceptance Filter 15 can be used as either an accep-

tance filter or an acceptance mask register. In addition

to three transmit and two receive buffers, there are six

more message buffers. One or more of these additional

buffers can be programmed as transmit or receive buff-

ers. These additional buffers can also be programmed

to automatically handle RTR messages.

Fourteen of sixteen acceptance filter registers can be

dynamically associated to any receive buffer and

acceptance mask register. One can use this capability

to associate more than one filter to any one buffer.

When a receive buffer is programmed to use standard

identifier messages, part of the full acceptance filter

the data byte filter is programmable from 0 to 18 bits.

This functionality simplifies implementation of high-level

protocols, such as the DeviceNet protocol.

The following is the list of resources available in Mode 1:

• Three transmit buffers: TXB0, TXB1 and TXB2

• Two receive buffers: RXB0 and RXB1

• Six buffers programmable as TX or RX: B0-B5

• Automatic RTR handling on B0-B5

• Sixteen dynamically assigned acceptance filters:

RXF0-RXF15

• Two dedicated acceptance mask registers;

RXF15 programmable as third mask:

RXM0-RXM1, RXF15

• Programmable data filter on standard identifier

messages: SDFLC

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