NS486SXL NSC [National Semiconductor], NS486SXL Datasheet - Page 18

• Manufacturer Part Number: NS486SXL
• Description: Optimized 32-Bit 486-Class Controller with On-Chip Peripherals for Embedded Systems
• Manufacturer: NSC [National Semiconductor]

www.national.com
t
t
t
t
Symbol
Symbol
PF
PR
VPG
PGV
Note 11: The rising/falling rate is assumed linear.
PWRGOOD and Power Rampdown Timing
Power Ramp Times
Note: The rising/falling rate is assumed linear.
AC Switching Specifications
The following pages list some of the preliminary AC Specifi-
cations for the NS486SXL. All parameters are listed in alpha-
betical order according to their Symbol.
The Tables consist of the following:
Parameter— A short description of the specification being
Symbol—
Formula—
Min—
Max—
How to calculate the actual specification at a given fre-
quency:
V
V
V
PWGOOD Falling to V
DD
DD
DD
Falling Time from 4.5V to 0V
Rising Time from 0V to 4.5V
(4.5V) to PWGOOD High
documented.
A quick reference between the timing dia-
gram and the Table entries.
An equation, which in addition to the Mini-
mum and Maximum Specifications can be
used to determine the actual timing provided
at any operating frequency.
Minimum Specification when added to the
value produced by the formula.
Maximum Specification when added to the
value produced by the formula.
DD
(Continued)
(4.5V)
TABLE 16. V
FIGURE 7. PWGOOD in Relation to V
TABLE 15. V
Parameter
Parameter
DD
DD
Rampdown vs PWRGOOD
Rise and Fall Times
18
In the formula column, one will see many formulae, which
contain the variable T. The T represents one period (or one
T-state) of the CPU Clock. So if the CPU is running at
25 MHz, T is equavalent to 40 ns; similarly if the CPU is run-
ning at 20 MHz, T is equavalent to 50 ns.
EXAMPLE: Calculate the minimum guaranteed Column Ad-
dress Setup Time.
As the frequency varies, so will many of the specifications.
One should always calculate the specification based on the
CPU’s operating frequency.
At 25 MHz
At 20 MHz
DD
Formula + Min Spec
(0.5T) + (−20 ns)
0.5 (40 ns) + (−20 ns)
20 ns - 20 ns
Formula + Min Spec
(0.5T) + (−20 ns)
0.5 (50 ns) + (−20 ns)
25 ns - 20 ns
Min
Min
5
5
1
1
DS100121-12
Max
Max
=
=
=
= 0 ns
=
=
=
= 5 ns
Units
Units
ms
ms
µs
µs