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Editors Chapter 3. Concepts

Almost Full Offset

(decimal)

This deﬁnes the word depth at which the FIFO almost full signal

is asserted. The almost full ﬂag is asserted when there are

(afull offset + 1) or fewer locations available to be written in the

FIFO. The almost full signal is asserted when the the difference

between the Write Pointer and the Read Pointer is greater than or

equal to the difference between the Maximum FIFO Depth and the

value of this ﬁeld (afull offset parameter).

Almost Empty

Offset (decimal)

This deﬁnes the word depth at which the FIFO almost empty

signal is asserted. The almost empty ﬂag is asserted when there

are (aempty offset - 1) or fewer words remaining in the FIFO. The

almost empty signal is asserted when the the difference between

the Write Pointer and the Read Pointer is less than the value of this

ﬁeld (aempty offset parameter).

First Word Fall Through Enabled When enabled, the ﬁrst value written into the FIFO appears at the

dout output without having to perform a read operation. If First

Word Fall Through is disabled, the ﬁrst data word written into the

FIFO is available at the FIFO output one rdclk clock cycle after the

ﬁrst read operation. This parameter only affects the availability of

the ﬁrst word written into the FIFO after an empty condition.

Operation of the two modes is the same after the ﬁrst read operation

is performed.

Synchronized Reset Mode When this is disabled, both the read and write pointers resets utilize

the Reset Synchronizer circuitry. When this option is enabled the

rstn input must be synchronous to the wrclk/rdclk clock

driving the FIFO.

Prevent Overﬂow/Underﬂow Enabling this option allows the user to read from the FIFO when the

FIFO is empty and write to the FIFO when it is full. Disabling this

safety check will allow the FIFO to run faster. Details can be found

in the user macro guide.

71 http://www.achronix.com UG001 Rev. 5.0 - 5th December 2012

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Achronix ACE Version 5.0 Bedienungsanleitung Seite 83