Achronix Speedster22i User Macro Guide - Manual (Page 97)

Registers DFFS
Speedster22i Macro Cell Library Achronix Semiconductor Proprietary PAGE 81
DFFS
Positive Clock Edge D-Type Register with Asynchronous Set
sn
d
ck
DFFS
q
Figure 2-15: Logic Symbol
DFFS is a single D‐type register with data input (d), clock (ck), and active‐low set (sn) inputs
and data (q) output. The active‐low set input overrides all other inputs when it is asserted low
and sets the data output high. If the asynchronous set input is not asserted, the data output is
set to the value on the data input upon the next rising edge of the clock.
Pins
Table 2-50: Pin Descriptions
Name Type Description
d Data input.
sn
Active-low asynchronous set input. A low on sn sets the q output high
independent of the other inputs.
ck Positive-edge clock input.
q
Data output. The value present on the data input is transferred to the q
output upon the rising edge of the clock if the asynchronous set input is
high.
Parameters
Table 2-51: Parameters
Parameter Defined Values Default Value
init 1’b1
sr_assertion “unclocked”
init
The init parameter defines the initial value of the output of the DFFS register. This is the value
the register takes upon the initial application of power to the FPGA. The default value of the
init parameter is 1’b1.
sr_assertion
The sr_assertion parameter defines the behavior of the output when the sn set input is
asserted. Assigning the sr_assertion to “unclocked” results in an asychronous assertion of the
reset signal, where the q output is set to one upon assertion of the active‐low reset signal.
Assigning the sr_assertion to “clocked” results in a synchronous assertion of the reset signal,
where the q output is set to one at the next rising edge of the clock. The default value of the
sr_assertion parameter is “unclocked”.
input
input
input
output
1’b0, 1’b1
“unclocked”, “clocked”