LAN8742AI-CZ datasheet(109/124 Pages) MICROCHIP

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 2013-2015 Microchip Technology Inc.

DS00001989A-page 109

LAN8742A/LAN8742Ai

5.6.3

POWER-ON nRST & CONFIGURATION STRAP TIMING

This diagram illustrates the nRST reset and configuration strap timing requirements in relation to power-on. A hardware

reset (nRST assertion) is required following power-up. For proper operation, nRST must be asserted for no less than

trstia. The nRST pin can be asserted at any time, but must not be deasserted before tpurstd after all external power sup-

plies have reached operational levels. In order for valid configuration strap values to be read at power-up, the tcss and

tcsh timing constraints must be followed. Refer to Section 3.8.6, "Resets" for additional information.

Note 1: 20 clock cycles for 25 MHz, or 40 clock cycles for 50 MHz

FIGURE 5-3:

POWER-ON nRST & CONFIGURATION STRAP TIMING

TABLE 5-11:

POWER-ON nRST & CONFIGURATION STRAP TIMING VALUES

Symbol

Description

Min.

Typ.

Max.

Unit

tpurstd

External power supplies at operational level to nRST

deassertion

tpurstv

External power supplies at operational level to nRST

valid

0ns

trstia

nRST input assertion time

100

µs

tcss

Configuration strap pins setup to nRST deassertion

200

tcsh

Configuration strap pins hold after nRST deassertion

totaa

Output tri-state after nRST assertion

todad

Output drive after nRST deassertion

800

(see Note 1)

Note:

nRST deassertion must be monotonic.

Note:

Device configuration straps are latched as a result of nRST assertion. Refer to Section 3.7, "Configuration

Straps" for details. Configuration straps must only be pulled high or low and must not be driven as inputs.

tcss

nRST

Configuration Strap

Pins Input

trstia

tcsh

Configuration Strap

Pins Output Drive

todad

All External

Power Supplies

tpurstd

Vopp

tpurstv

totaa

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