EVB8710 Evaluation Board User Manual
Revision 1.1 (05-24-10) USER MANUAL SMSC EVB8710
6
2.2.3 nINT/TXER/TXD4 Pin Configuration (nINTSEL)
The nINT, TXER, and TXD4 functions share a common LAN8710A pin. This pin can operate in two
functional modes: nINT (Interrupt) Mode and TXER/TXD4 Mode. The nINTSEL configuration strap is
used to select one of these two modes. The EVB8710 must be properly configured for each mode as
follows:
nINT Mode (Default EVB8710 Mode)
Populate the 1-2 positions of R42 and R43 to pull-up the nINTSEL strap (nINT mode).
Depopulate the 2-3 positions of R42 and R43.
Depopulate R46.
TXER/TXD4 Mode
Populate the 2-3 positions of R42 and R43 to pull-down the nINTSEL strap (TXER/TXD4 mode).
Depopulate the 1-2 positions of R42 and R43.
Populate R46.
Note: The nINTSEL configuration strap shares functionality with LED2. Therefore, LED2 may function
active-high or active-low depending on the nINTSEL configuration. For additional information
on the functionality of the nINT/TXER/TXD4 and LED2/nINTSEL pins, refer to the LAN8710A
Datasheet and LAN8710A schematics.
2.2.4 Internal +1.2V Regulator Configuration (REGOFF)
The LAN8710A provides the ability to disable the internal +1.2V regulator. When the regulator is
disabled, an external +1.2V must be supplied to the VDDCR pin (via TP3). Configuration of the internal
regulator is controlled by the REGOFF configuration strap. The EVB8710 must be properly configured
for each mode as follows:
Internal +1.2V Regulator Enabled (Default EVB8710 Mode)
Populate the 1-2 positions of R40 and R41 to pull-down the REGOFF strap (enable regulator).
Depopulate the 2-3 positions of R40 and R41.
Internal +1.2V Regulator Disabled
Populate the 2-3 positions of R40 and R41 to pull-up the REGOFF strap (disable regulator).
Depopulate the 1-2 positions of R40 and R41.
Note: The REGOFF configuration strap shares functionality with LED1. Therefore, LED1 may
function active-high or active-low depending on the REGOFF configuration. For additional
information on the LED1/REGOFF pin and the disabling of the internal 1.2V regulator (power
sequencing requirements, etc.), refer to the LAN8710A Datasheet and LAN8710A schematics.
2.2.5 Clock Configuration
The EVB8710 can be clocked via the onboard crystal oscillator or an optional external clock.
Crystal Oscillator (Default)
The 25 MHz crystal Y1 is connected to the internal oscillator of the LAN8710A. A PLL circuit in the
LAN8710A generates all the timing required by the PHY.
External Clock
The EVB8710 can be configured to use an external clock by removing crystal Y1 and resistor R20. A
25MHz +3.3V signal may then be applied to pin 1 of Y1 (which connects to pin 5 of the LAN8710A).
Pin 2 of Y1 (which connects to pin 4 of the LAN8710A) should be left floating when using an external
clock.