
Chapter 9. Slave FIFOs Page 9-5
Figure 9-5. 16-bit Mode Slave FIFOs, WORDWIDE=1
9.2.3 Interface Clock (IFCLK)
The slave FIFO interface can be clocked from either an internal or an external source. The FX2’s
internal clock source can be configured to run at either 30 or 48 MHz, and it can optionally be out-
put on the IFCLK pin. If the FX2 is configured to use an external clock source, the IFCLK pin can
be driven at any frequency between 5 MHz and 48 MHz. On power-on reset, the FX2 defaults to
the internal source at 48 MHz, normal polarity, with the IFCLK output disabled. See Figur e9-6.
IFCONFIG.7 selects between internal and external sources: 0 = external, 1 = internal.
IFCONFIG.6 selects between the 30- and 48-MHz internal clock: 0 = 30 MHz, 1 = 48 MHz. This bit
has no effect when IFCONFIG.7 = 0.
IFCONFIG.5 is the output enable for the internal clock source: 0 = disable, 1 = enable. This bit has
no effect when IFCONFIG.7 = 0.
IFCONFIG.4 inverts the polarity of the interface clock (whether it’s internal or external): 0 = normal,
1 = inverted. IFCLK inversion can make it easier to interface the FX2 with certain external circuitry;
Figure 9-7, for example, demonstrates the use of IFCLK inversion in order to ensure a long-
enough setup time for reading the FX2’s FIFO flags.
When IFCLK is configured as an input, the minimum frequency that can be applied to it is 5 MHz.
30/48MHz
FLAGA
FIFOADR[1:0]
Slave FIFOsFX2 Registers Device Pins
FLAGB
FLAGC
FLAGD/SLCS#
SLOE
SLRD
SLWR
PKTEND
FD[15:0]
EP4FIFOBUF
EP6FIFOBUF
EP8FIFOBUF
EP2FIFOBUF
EP8
EP6
EP4
EP2
IFCLK
5 - 48MHz
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