LAN9250 datasheet(54/421 Pages) MICROCHIP

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LAN9250

DS00001913A-page 54

 2015 Microchip Technology Inc.

7.0

CONFIGURATION STRAPS

Configuration straps allow various features of the device to be automatically configured to user defined values. Config-

uration straps can be organized into two main categories: Hard-Straps and Soft-Straps. Both hard-straps and soft-straps

are latched upon Power-On Reset (POR), or pin reset (RST#). The primary difference between these strap types is that

soft-strap default values can be overridden by the EEPROM Loader, while hard-straps cannot.

Configuration straps which have a corresponding external pin include internal resistors in order to prevent the signal

from floating when unconnected. If a particular configuration strap is connected to a load, an external pull-up or pull-

down resistor should be used to augment the internal resistor to ensure that it reaches the required voltage level prior

to latching. The internal resistor can also be overridden by the addition of an external resistor.

7.1

Soft-Straps

Soft-strap values are latched on the release of POR or RST# and are overridden by values from the EEPROM Loader

(when an EEPROM is present). These straps are used as direct configuration values or as defaults for CPU registers.

Some, but not all, soft-straps have an associated pin. Those that do not have an associated pin, have a tie off default

value. All soft-strap values can be overridden by the EEPROM Loader. Refer to Section 13.4, "EEPROM Loader," on

page 290 for information on the operation of the EEPROM Loader and the loading of strap values. Table 13-4,

“EEPROM Configuration Bits,” on page 292 defines the soft-strap EEPROM bit map.

Straps which have an associated pin are also fully defined in Section 3.0, "Pin Descriptions and Configuration," on

page 10.

Table 7-1 provides a list of all soft-straps and their associated pin or default value.

Upon setting the Digital Reset (DIGITAL_RST) bit in the Reset Control Register (RESET_CTL) or upon issuing a

RELOAD command via the EEPROM Command Register (E2P_CMD), these straps return to their original latched (non-

overridden) values if an EEPROM is no longer attached or has been erased. The associated pins are not re-sampled

(i.e. the value latched on the pin during the last POR or RST# will be used, not the value on the pin during the digital

reset or RELOAD command issuance). If it is desired to re-latch the current configuration strap pin values, a POR or

RST# must be issued.

Note:

The system designer must guarantee that configuration strap pins meet the timing requirements specified

in Section 19.6.3, "Reset and Configuration Strap Timing". If configuration strap pins are not at the correct

voltage level prior to being latched, the device may capture incorrect strap values.

Note:

The use of the term “configures” in the “Description” section of Table 7-1 indicates the register bit is loaded

with the strap value, while the term “Affects” means the value of the register bit is determined by the strap

value and some other condition(s).

TABLE 7-1:

SOFT-STRAP CONFIGURATION STRAP DEFINITIONS

Strap Name

Description

Pin / Default Value

LED_en_strap[2:0]

LED Enable Straps:

Configures the default value for the LED

Enable 2-0 (LED_EN[2:0]) bits of the LED Configuration

111b

LED_fun_strap[2:0]

LED Function Straps:

Configures the default value for the

LED Function 2-0 (LED_FUN[2:0]) bits of the LED

Configuration Register (LED_CFG).

000b

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