LFXP3E-4TN100C Lattice, LFXP3E-4TN100C Datasheet - Page 202

• Manufacturer Part Number: LFXP3E-4TN100C
• Description: IC FPGA 3.1KLUTS 62I/O 100-TQFP
• Manufacturer: Lattice

Specifications of LFXP3E-4TN100C

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Memory Usage Guide
Lattice Semiconductor
LatticeECP/EC and LatticeXP Devices
Dual Clock First In First Out (FIFO_DC) Memory: The FIFO_DC or the dual clock FIFO is also an emulated
FIFO. Again the address logic and the flag logic is implemented in the FPGA fabric around the RAM.
The ports available on the FIFO_DC are:
• Reset
• RPReset
• WrClock
• RdClock
• WrEn
• RdEn
• Data
• Q
• Full Flag
• Almost Full Flag
• Empty Flag
• Almost Empty Flag
FIFO_DC Flags: FIFO_DC, as an emulated FIFO, required the flags to be implemented in the FPGA logic around
the block RAM. Because of the two clocks, the flags are required to change clock domains from read clock to write
clock and vice versa. This adds latency to the flags either during assertion or during de-assertion. The latency can
be avoided only in one of the cases (either assertion or de-assertion).
In the current emulated FIFO, there is no latency during assertion of these flags. Thus, when these flag go true,
there is no latency. However this causes the latency during the de-assertion.
Let us assume that we start to write into the FIFO_DC to fill it. The write operation is controlled by WrClock and
WrEn, however it takes extra RdClock cycles for de-assertion of Empty and Almost Empty flags.
On the other hand, de-assertion of Full and Almost Full result in reading out the data from the FIFO_DC. It takes
extra WrClock cycles after reading the data for these flags to come out.
With this in mind, let us look at the FIFO_DC without output register waveforms. Figure 9-42 shows the operation of
the FIFO_DC when it is empty and the data starts to get written into it.
9-37