NS486SXL Datasheet, PDF(18/26 Page) National Semiconductor (TI) – Optimized 32-Bit 486-Class Controller with On-Chip Peripherals for Embedded Systems

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

NS486SXL Datasheet, PDF (18/26 Pages) National Semiconductor (TI) – Optimized 32-Bit 486-Class Controller with On-Chip Peripherals for Embedded Systems

◁

Power Ramp Times (Continued)

TABLE 15. VDD Rise and Fall Times

Symbol

tPF

VDD Falling Time from 4.5V to 0V

tPR

VDD Rising Time from 0V to 4.5V

Note 11: The rising/falling rate is assumed linear.

Parameter

PWRGOOD and Power Rampdown Timing

TABLE 16. VDD Rampdown vs PWRGOOD

Symbol

tVPG

tPGV

VDD (4.5V) to PWGOOD High

PWGOOD Falling to VDD (4.5V)

Parameter

Min

Max

Units

Min

Max

Units

Âµs

Note: The rising/falling rate is assumed linear.

FIGURE 7. PWGOOD in Relation to VDD

DS100121-12

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:

Parameterâ A short description of the specification being

documented.

Symbolâ

A quick reference between the timing dia-

gram and the Table entries.

Formulaâ

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.

Minâ

Minimum Specification when added to the

value produced by the formula.

Maxâ

Maximum Specification when added to the

value produced by the formula.

How to calculate the actual specification at a given fre-

quency:

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.

At 25 MHz Formula + Min Spec

(0.5T) + (â20 ns)

0.5 (40 ns) + (â20 ns)

20 ns - 20 ns

= 0 ns

At 20 MHz Formula + Min Spec

(0.5T) + (â20 ns)

0.5 (50 ns) + (â20 ns)

25 ns - 20 ns

= 5 ns

As the frequency varies, so will many of the specifications.

One should always calculate the specification based on the

CPUâs operating frequency.

www.national.com

▷