Specifying Time Delay in TS Attributes

Nanoseconds are the default units for specifying delay times in TS attributes. However, after specifying the maximum delay or minimum frequency numerically, you can enter the unit of measure by specifying the following.

• PS for picoseconds, NS for nanoseconds, US for microseconds, or MS for milliseconds
  
  
• MHZ for megahertz, KHZ for kilohertz, or GHz for gigahertz
  
  

As an alternate way of specifying time delay, you can specify one time delay in terms of another. Instead of specifying a time or frequency in a TS attribute definition, you can specify a multiple or division of another TS attribute. This is useful in a system where all clocks are derived from a master clock; in this situation, changing the timing specification for the master clock changes the specification for all clocks in the system.

Use the syntax below to specify a TS attribute delay in terms of another.

Schematic syntax attached to TIMESPEC primitive

TSidentifier=specification reference_TS_attribute[{*|/}number]

UCF syntax

TIMESPEC TSidentifier=specification reference_TS_attribute[{*|/}number];

number can be either a whole number or a decimal. The specification can be any From-To statement as illustrated by the following examples.

FROM PADS TO PADS
FROM group1 TO group2
FROM tnm_identifier TO FFS
FROM LATCHES TO group1

Use “*” to represent multiplication and “/” to represent division. The specification type of the reference TS attribute does not need to be the same as the TS attribute being defined; however, it must not be specified in terms of TIG.

Examples of specifying a TS attribute in terms of another are as follows. In these cases, assume that the reference attributes were specified as delays (not frequencies).

In the example below, the paths between flip-flops and pads are placed and routed so that their delay is at most 10 times the delay specified in the TS05 attribute.

Schematic syntax in TIMESPEC primitive

TS08=FROM FFS TO PADS TS05*10

UCF syntax

TIMESPEC TS08=FROM FFS TO PADS TS05*10;

In the example below, the paths between input and output pads are placed and routed so that their delay is at most one-eighth the delay specified in the TS07 attribute.

Schematic syntax in TIMESPEC primitive

TS1=FROM PADS TO PADS TS07/8

UCF syntax

TIMESPEC TS1=FROM PADS TO PADS TS07/8;

Note: When a reference attribute is specified as a frequency, a multiple represents a faster specification; a division represents a slower specification.

You can also specify a TS attribute in terms of a TS attribute that is already a specification of another. The following example provides an illustration.

Schematic syntax in TIMESPEC primitive

TS09=FROM FFS TO FFS 50
TS10=FROM FFS TO PADS TS09*2
TS11=FROM PADS TO PADS TS10*4

UCF syntax

TIMESPEC TS09=FROM FFS TO FFS 50;
TIMESPEC TS10=FROM FFS TO PADS TS09*2;
TIMESPEC TS11=FROM PADS TO PADS TS10*4;