RXB0D2 datasheet(16/92 Pages) MICROCHIP

16 / 92 page

MCP2515

DS21801G-page 16

 2003-2012 Microchip Technology Inc.

3.5

TXnRTS PINS

The TXnRTS pins are input pins that can be configured

as:

• Request-to-send inputs, which provide an

alternative means of initiating the transmission of

a message from any of the transmit buffers

• Standard digital inputs

Configuration and control of these pins is accomplished

using the TXRTSCTRL register (see Register 3-3). The

TXRTSCTRL register can only be modified when the

MCP2515 is in Configuration mode (see Section 10.0

“Modes of Operation”). If configured to operate as a

request-to-send pin, the pin is mapped into the

respective TXBnCTRL.TXREQ bit for the transmit

buffer. The TXREQ bit is latched by the falling edge of

the TXnRTS pin. The TXnRTS pins are designed to

allow them to be tied directly to the RXnBF pins to

automatically initiate a message transmission when the

RXnBF pin goes low.

The TXnRTS pins have internal pull-up resistors of

100 k

 (nominal).

3.6

Aborting Transmission

The MCU can request to abort a message in a specific

message

buffer

clearing

the

associated

TXBnCTRL.TXREQ bit.

In addition, all pending messages can be requested to

be aborted by setting the CANCTRL.ABAT bit. This bit

MUST be reset (typically after the TXREQ bits have

been verified to be cleared) to continue transmitting

messages. The TXBnCTRL.ABTF flag will only be set

if the abort was requested via the CANCTRL.ABAT bit.

Aborting a message by resetting the TXREQ bit does

NOT cause the ABTF bit to be set.

Note 1: Messages that were transmitting when

the abort was requested will continue to

transmit.

the

message

does

not

successfully complete transmission (i.e.,

lost arbitration or was interrupted by an

error frame), it will then be aborted.

2: When One-Shot mode is enabled, if the

message is interrupted due to an error

frame

loss

arbitration,

the

TXBnCTRL.ABTF bit will set.

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