Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface
Datasheet
Revision 1.4 (08-19-08)
36
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
. 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
Timer & Free-Running Clock," on page 162
for additional details.
Note:
Crystal specifications are provided in
Table 15.15, “LAN9311/LAN9311iCrystal Specifications,”
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:
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
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.
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.