Datasheet

MCP2515
DS20001801J-page 16  2003-2019 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 3-2). 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 TXREQ bit (TXBnCTRL[3]) 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 by clearing the associated TXREQ bit.
In addition, all pending messages can be requested to
be aborted by setting the ABAT bit (CANCTRL[4]). This
bit MUST be reset (typically after the TXREQ bits have
been verified to be cleared) to continue transmitting
messages. The ABTF flag (TXBnCTRL[6]) will only be
set if the abort was requested via the ABAT bit. Abort-
ing 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. If the message does not suc-
cessfully 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 or loss of arbitration, the ABTF bit
will set.