
Chapter 9. Slave FIFOs Page 9-7
equally useful for either type of endpoint (it can, for instance, give advance warning that an OUT
endpoint is almost empty or that an IN endpoint is almost full).
The FLAGA, FLAGB, and FLAGC pins can operate in either of two modes: Indexed or Fixed, as
selected via the PINFLAGSAB and PINFLAGSCD registers. The FLAGD pin operates in Fixed
mode only. Each pin is configured independently; some pins can be in Fixed mode while others are
in Indexed mode. See Chapter 15, "Registers," for complete details.
Flag pins configured for Indexed mode report the status of the FIFO currently selected by the
FIFOADR[1:0] pins. When configured for Indexed mode, FLAGA reports the “programmable-level”
status, FLAGB reports the “full” status, and FLAGC reports the “empty” status.
Flag pins configured for Fixed mode report one of the three conditions for a specific FIFO, regard-
less of the state of the FIFOADR[1:0] pins. The condition and FIFO are user-selectable. For exam-
ple, FLAGA could be configured to report FIFO2’s “empty” status, FLAGB to report FIFO4’s
“empty” status, FLAGC to report FIFO4’s “programmable level” status, and FLAGD to report
FIFO6’s “full” status.
The polarity of the “empty” and “full” flag pins defaults to active-low but may be inverted via the
FIFOPINPOLAR register.
At power-on reset, the FIFO flags are configured for Indexed operation.
Figure 9-8. FLAGx
FLAGA
FIFOADR[1:0]
Slave FIFOs FX2 Registers Device Pins
FLAGB
FLAGC
SLOE
SLRD
SLWR
PKTEND
FD[15:0]
EP4FIFOBUF
EP6FIFOBUF
EP8FIFOBUF
EP2FIFOBUF
EP8
EP6
EP4
EP2
IFCLK
30/48MHz
5 - 48MHz
FLAGD/SLCS#
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