XC886/888CLM
Controller Area Network (MultiCAN) Controller
User’s Manual
15-37
V1.3, 2010-02
MultiCAN, V1.0
15.1.9.6
Transmit FIFO
The Transmit FIFO structure is used to buffer a series of data or remote frames that must
be transmitted.
A Transmit FIFO is selected by setting MOFCRn.MMC = 0010
B
in the FIFO base object.
Unlike the Receive FIFO, slave objects assigned to the Transmit FIFO are required to
set explicitly their bit fields MOFCRn.MMC = 0011
B
. The CUR pointer in all slave objects
must point back to the Transmit FIFO Base Object (to be initialized by software).
The MOSTATn.TXEN1 bits (Transmit Enable 1) of all message objects except the one
which is selected by the CUR pointer of the base object must be cleared by software.
TXEN1 of the message (slave) object selected by CUR must be set. CUR (of the base
object) may be initialized to any FIFO slave object.
When tagging the message objects of the FIFO as valid to start the operation of the
FIFO, then the base object must be tagged valid (MSGVAL = 1) first.
Before a Transmit FIFO becomes de-installed during operation, its slave objects must
be tagged invalid (MSGVAL = 0).
The Transmit FIFO uses the bit MOCTRn.TXEN1 of all FIFO elements to select the
actual message for transmission. Transmit acceptance filtering evaluates TXEN1 for
each message object and a message object can win transmit acceptance filtering only if
its TXEN1 bit is set. When a FIFO object has transmitted a message, the hardware
clears its TXEN1 bit in addition to standard transmit postprocessing (clear TXRQ,
transmit interrupt etc.) and moves the CUR pointer to the next message object to be
transmitted. TXEN1 is set automatically (by hardware) in the next message object. Thus,
TXEN1 moves along the Transmit FIFO structure like a token that selects the active
element.
If bit field MOFCRn.OVIE (“Overflow Interrupt Enable”) of the FIFO base object is set and
the current pointer CUR becomes equal to MOFGPRn.SEL, a FIFO overflow interrupt
request is generated. The interrupt request is generated on interrupt node RXINP of the
base object after postprocessing of the received frame. Receive interrupts are still
generated for the Transmit FIFO base object if bit RXIE is set.
*
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