External SetUp and Hold Times
Last Edit July 22, 2001
Case 2: When The Timing Specifications Are WorstCase
For the case where the vendor has specified timing delays as worstcase,
the following procedures can be applied. Note that if the macro intrinsic
delays are specified as worstcase maximum, some means of computing the
worstcase minimum for the same operating conditions must exist.
SetUp Time  Generic Equation
When computing the setup time, it is desirable to assume that the data
propagation path delay is the worstcase maximum and that the clock path
propagation delay is a worstcase minimum for the operating conditions.
The generic equation is:
t_{suexternal} = t_{Dmax}
 t_{Cmin} + T_{sumacromax}

Hold Time  Generic Equation
When computing the hold time, it is desirable to assume that the data
propagation path delay is the worstcase minimum and that the clock path
propagation delay is a worstcase maximum for the operating conditions.
The generic equation is:
t_{hexternal} = t_{Cmax}
 t_{Dmin} + T_{hmacromax}

Example  The AMCC BiCMOS Q14000 Series
The Q14000 Series has a complex arrangement of worstcase multipliers,
separating interface and internal and differentiating between the channelled
and channelless arrays. For the Q14000 BiCMOS arrays, the data and clock
paths are broken down into the interface macro and its net (t_{Dinput}
or t_{Cinput}), and the internal macros and the nets
they drive (t_{D} or t_{C}). Both setup and hold times
are specified as nominal for this array.
For the Q14000 Series and its dual multipliers, the external setup and
hold time equations become:
Table 61 General Equations When WorstCase Multipliers Are Used
t_{suexternal} for Q14000 BiCMOS
WCM_{maxinterface} * t_{Dinput}
+ WCM_{maxcore} * t_{D}  WCM_{mininterface}*
t_{Cinput}  WCM_{mincore}*
t_{C} + WCM_{maxcore} * Tsu_{(macro)}
t_{hexternal} for Q14000 BiCMOS
WCM_{maxinterface}* t_{Cinput}
+ WCM_{maxcore} * t_{C}  WCM_{mininterface}*
t_{Dinput}  WCM_{mincore}*
t_{D} + WCM_{maxcore} * Th_{(macro)}

Table 62 provides the external setup and hold equations for
the Q14000 BiCMOS Series Arrays for four defined operating conditions,
MIL, COM5, COM4 and MIN, using the specified worstcase delay multipliers
specified for the array series for those conditions.
Note that, since these arrays specify nominal macro intrinsic setup
and hold times, the worstcase time delay multipliers are applied to the
setup and hold times as well as to the Tpd delays. This may not always
be the case. (Refer to the AMCC Q5000 and Q14000 Design Manuals.)
Table 62 SetUp And Hold Equations BiCMOS Q14000 Series Arrays Q28000B,
Q14000B, Q6000B And Q800B Arrays
MILITARY
OPERATING
RANGE
MIL4
or
MIL5

t_{suexternal} = 1.70 * t_{Dinput}
+ 1.95 * t_{D}  1.40 * t_{Cinput}  1.59
* t_{C} + 1.95 * Tsu_{(macro)}
t_{hexternal} = 1.70 * t_{Cinput}
+ 1.95 * t_{C}  1.40 * t_{Dinput} 
1.59 * t_{D} + 1.95 * Th_{(macro)}

COMMERCIAL
OPERATING
RANGE
COM5

t_{suexternal} = 1.55 * t_{Dinput}
+ 1.55 * t_{D}  1.27 * t_{Cinput}  1.27
* t_{C} + 1.55 * Tsu_{(macro)}
t_{hexternal} = 1.55 * t_{Cinput}
+ 1.55 * t_{C}  1.27 * t_{Dinput} 
1.27 * t_{D} + 1.55 * Th_{(macro)}

COMMERCIAL
OPERATING
RANGE
COM4

t_{suexternal} = 1.55 * t_{Dinput}
+ 1.75 * t_{D}  1.27 * t_{Cinput}  1.43
* t_{C} + 1.75 * Tsu_{(macro)}
t_{hexternal} = 1.55 * t_{Cinput}
+ 1.75 * t_{C}  1.27 * t_{Dinput} 
1.43 * t_{D} + 1.75 * Th_{(macro)}

MINIMUM

t_{suexternal} = 0.86 * (t_{D} + t_{Dinput})
 0.70 * (t_{C} + t_{Cinput}) + 0.86 *
Tsu_{(macro)}
t_{hexternal} = 0.86 * (t_{C} + t_{Cinput})
 0.70 * (t_{D} + t_{Dinput}) 0.86 *
Th_{(macro)}

These equations are for the channelless arrays, those designed with a
seaofgates or seaofcells architecture. (Refer to the AMCC Q14000 Design
Manual for the equations for the other arrays in the series that are channelled.)
Which Equations Should be Used?
For external setup time, use the following as a guideline:
 Use the MILITARY or COMMERCIAL equations for external setup time
when
( t_{D} + t_{Dinput})  0.82 * (t_{C}
+ t_{Cinput}) > 0.
 Use the MINIMUM equations for external setup time when
(t_{D} + t_{Dinput})  0.82 * (t_{C}
+ t_{Cinput}) < 0.
For external hold time, use the following as a guideline:
 Use the MILITARY or COMMERCIAL equations for external hold time when
(t_{C} + t_{Cinput})  0.82 * (t_{D}
+ t_{Dinput}) > 0.
 Use the MINIMUM equations for external hold time when
(t_{C} + t_{Cinput})  0.82 * (t_{D}
+ t_{Dinput}) < 0.
.
