RXB0D2 datasheet(60/92 Pages) MICROCHIP

60 / 92 page

MCP2515

DS21801G-page 60

 2003-2012 Microchip Technology Inc.

10.4

Loopback Mode

Loopback 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 be in a recessive state.

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 CANCTRL register.

10.5

Normal Mode

Normal mode is the standard operating mode of the

MCP2515. In this mode, the device actively monitors all

bus messages and generates Acknowledge bits, error

frames, etc. This is also the only mode in which the

MCP2515 will transmit messages over the CAN bus.

CANCTRL – CAN CONTROL REGISTER

(ADDRESS: XFh)

R/W-1

R/W-0

R/W-1

REQOP2

REQOP1

REQOP0

ABAT

OSM

CLKEN

CLKPRE1

CLKPRE0

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7-5

REQOP<2:0>: Request Operation mode bits

000

Set Normal Operation mode

001

Set Sleep mode

010

Set Loopback mode

011

Set Listen-Only mode

100

Set Configuration mode

All other values for REQOP bits are invalid and should not be used

On power-up, REQOP = b’111’

bit 4

ABAT: Abort All Pending Transmissions bit

= Request abort of all pending transmit buffers

= Terminate request to abort all transmissions

bit 3

OSM: One-Shot mode bit

= Enabled. Message will only attempt to transmit one time

= Disabled. Messages will reattempt transmission, if required

bit 2

CLKEN: CLKOUT Pin Enable bit

= CLKOUT pin enabled

= CLKOUT pin disabled (Pin is in high-impedance state)

bit 1-0

CLKPRE<1:0>: CLKOUT Pin Prescaler bits

=FCLKOUT = System Clock/1

=FCLKOUT = System Clock/2

=FCLKOUT = System Clock/4

=FCLKOUT = System Clock/8

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