LAN9311 datasheet(36/459 Pages) SMSC

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Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface

Datasheet

Revision 1.6 (08-18-09)

SMSC LAN9311/LAN9311i

DATASHEET

Chapter 4 Clocking, Resets, and Power Management

4.1

Clocks

The LAN9311/LAN9311i includes a clock module which provides generation of all system clocks as

required by the various sub-modules of the device. The LAN9311/LAN9311i requires a fixed-frequency

25MHz clock source for use by the internal clock oscillator and PLL. This is typically provided by

attaching a 25MHz crystal to the XI and XO pins as specified in Section 15.6, "Clock Circuit," on

page 454. Optionally, this clock can be provided by driving the XI input pin with a single-ended 25MHz

clock source. If a single-ended source is selected, the clock input must run continuously for normal

device operation. The internal PLL generates a fixed 200MHz base clock which is used to derive all

LAN9311/LAN9311i sub-system clocks.

In addition to the sub-system clocks, the clock module is also responsible for generating the clocks

used for the general purpose timer and free-running clock. Refer to Chapter 12, "General Purpose

Timer & Free-Running Clock," on page 162 for additional details.

Note: Crystal specifications are provided in Table 15.15, “LAN9311/LAN9311iCrystal Specifications,”

on page 454.

4.2

Resets

The LAN9311/LAN9311i provides multiple hardware and software reset sources, which allow varying

levels of the LAN9311/LAN9311i to be reset. All resets can be categorized into three reset types as

described in the following sections:

Chip-Level Resets

—Power-On Reset (POR)

—nRST Pin Reset

Multi-Module Resets

—Digital Reset (DIGITAL_RST)

—Soft Reset (SRST)

Single-Module Resets

—Port 2 PHY Reset

—Port 1 PHY Reset

—Virtual PHY Reset

The LAN9311/LAN9311i supports the use of configuration straps to allow automatic custom

configurations of various LAN9311/LAN9311i parameters. These configuration strap values are set

upon de-assertion of all chip-level resets and can be used to easily set the default parameters of the

chip at power-on or pin (nRST) reset. Refer to Section 4.2.4, "Configuration Straps," on page 40 for

detailed information on the usage of these straps.

Note: The LAN9311/LAN9311i EEPROM Loader is run upon a power-on reset, nRST pin reset, and

digital reset. Refer to Section 10.2.4, "EEPROM Loader," on page 150 for additional

information.

Table 4.1 summarizes the effect of the various reset sources on the LAN9311/LAN9311i. Refer to the

following sections for detailed information on each of these reset types.

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