LX256VCF2085 datasheet(15/72 Pages) LATTICE

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Lattice Semiconductor

ispGDX2 Family Data Sheet

Figure 12. ispGDX2 FIFO Signals

Read Clock and Read Enable are the same as the Clock and Clock Enable signals of the input registers of the

associated MRB. These registers are used to register the FIFO outputs, and in modes that utilize the FIFO are con-

ﬁgured to use the same clock and clock enable signals. The Write Clock is selected from one of the GCLK/CE sig-

nals or the RECCLK (Recovered Clock) signal from the associated SERDES. The Write Enable is selected from

one of the local MRB product term CLK/CE signals. All FIFO operations occur on the rising edge of the clock

although clock polarity of these signals can be programmed.

The ﬂags from the FIFO, FULL, EMPTY and STRDb (Start Read) are each fed via a MUX in the MRB to an I/O

buffer. The STRDb (half full) signal is used in conjunction with SERDES. STRDb is an active low signal, the signal

is inactive (high) on FIFO RESET. After the FIFO reset when the FIFO contains data in ﬁve memory locations, at

the following write clock transition the STRDb becomes active (low). Note, if the Read Clocks arrive before writing

the sixth location, it may take longer than ﬁve write clocks before the STRDb becomes active. When the FIFO has

data in the ﬁrst six locations, at the next write clock transition the STRDb becomes inactive (high). Again, if the

Read Clocks arrive before writing the seventh location, the STRDb may stay active for longer than one write clock

period, even if the FIFO contains data in less than ﬁve locations. After this event, the STRDb stays inactive until the

FIFO is RESET again. STRDb does not become active again even if less than six memory locations are occupied

in the FIFO. It is the user’s responsibility to monitor the FULL and EMPTY signals to avoid data underﬂow/overﬂow

and to take appropriate actions.

Figure 13 shows how the FIFO is connected between the I/O banks and the GDX Blocks in FIFO mode. For more

information on the FIFO, please refer to Lattice technical note number TN1020, sysHSI Usage Guidelines.

FIFO

10x15

Data In (DIN)

Data Out (DOUT)

Write Clock (WCLK)

Write Enable (WE)

Full (FULL)

Empty (EMPTY)

Read Clock (RCLK)

Read Enable (RE)

Global Reset (RESETb)

Power-on Reset (PORb)

FIFO Reset (FIFORSTb)

Start Read (STRDb)

LX256VCF2085 Datasheet(PDF) 15 Page - Lattice Semiconductor