LAN9313 Datasheet, PDF (45/398 Pages) SMSC Corporation – Three Port 10/100 Managed Ethernet Switch with MII

Three Port 10/100 Managed Ethernet Switch with MII
Datasheet
4.2.4 Configuration Straps
Configuration straps allow various features of the LAN9313/LAN9313i to be automatically configured
to user defined values. Configuration 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
(nRST). 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 14.5.2, "Reset and Configuration Strap Timing," on page 390.
If configuration strap pins are not at the correct voltage level prior to being latched, the
LAN9313/LAN9313i may capture incorrect strap values.
4.2.4.1
Soft-Straps
Soft-strap values are latched on the release of POR or nRST 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. Table 4.2 provides a list of all soft-straps and their associated pin or default value.
Straps which have an associated pin are also fully defined in Chapter 3, "Pin Description and
Configuration," on page 26. Refer to Section 8.2.4, "EEPROM Loader," on page 113 for information on
the operation of the EEPROM Loader and the loading of strap values.
Upon setting the 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 nRST
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 nRST must be issued.
Table 4.2 Soft-Strap Configuration Strap Definitions
STRAP NAME
LED_en_strap[7:0]
LED_fun_strap[1:0]
DESCRIPTION
PIN / DEFAULT
VALUE
LED Enable Straps: Configures the default value for the
LED_EN bits in the LED Configuration Register
(LED_CFG). A high value configures the associated
LED/GPIO pin as a LED. A low value configures the
associated LED/GPIO pin as a GPIO.
Note:
One pin configures the default for all 8
LED/GPIOs, but 8 separate bits are loaded by the
EEPROM Loader, allowing individual control over
each LED/GPIO.
LED Function Straps: Configures the default value for the
LED_FUN bits in the LED Configuration Register
(LED_CFG). When configured low, the corresponding bit
will be cleared. When configured high, the corresponding
bit will be set.
LED_EN
LED_FUN[1:0]
SMSC LAN9313/LAN9313i
45
DATASHEET
Revision 1.2 (04-08-08)