LAN9353 Datasheet, PDF (67/523 Pages) Microchip Technology – Interfaces at up to 200Mbps via Turbo MII

LAN9353
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.
Note:
The system designer must guarantee that configuration strap pins meet the timing requirements specified
in Section 20.6.3, "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.
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 12.4, "EEPROM Loader," on
page 353 for information on the operation of the EEPROM Loader and the loading of strap values. Table 12-4,
“EEPROM Configuration Bits,” on page 355 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.
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).
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.
TABLE 7-1: SOFT-STRAP CONFIGURATION STRAP DEFINITIONS
Strap Name
LED_en_strap[5:0]
LED_fun_strap[2:0]
I2C_addr_override_strap
I2C_address_strap[6:0]
Description
Pin / Default Value
LED Enable Straps: Configures the default value for the LED
Enable 5-0 (LED_EN[5:0]) bits of the LED Configuration
Register (LED_CFG).
111111b
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).
I²C Address Override Strap: When set, the I²C slave uses
the address given by I2C_address_strap[6:0].
I_I²₂C_C
Address Straps: When I2C_addr_override_strap
slave uses this address.
set,
the
000b
0
0001010b
 2015 Microchip Technology Inc.
DS00001925A-page 67