DP83849C Datasheet, PDF (11/96 Pages) National Semiconductor (TI) – DUAL Commercial Temperature Dual Port 10/100 Mb/s Ethernet Physical Layer Transceiver

1.3 Clock Interface
Signal Name
X1
X2
CLK2MAC
Type
I
O
O
Pin #
70
69
68
Description
CRYSTAL/OSCILLATOR INPUT: This pin is the primary clock
reference input for the DP83849C and must be connected to a 25
MHz 0.005% (+50 ppm) clock source. The DP83849C supports
either an external crystal resonator connected across pins X1 and
X2, or an external CMOS-level oscillator source connected to pin
X1 only.
RMII REFERENCE CLOCK: This pin is the primary clock refer-
ence input for the RMII mode and must be connected to a 50 MHz
0.005% (+50 ppm) CMOS-level oscillator source.
CRYSTAL OUTPUT: This pin is the primary clock reference out-
put to connect to an external 25 MHz crystal resonator device.
This pin must be left unconnected if an external CMOS oscillator
clock source is used.
CLOCK TO MAC:
In MII mode, this pin provides a 25 MHz clock output to the sys-
tem.
In RMII mode, this pin provides a 50 MHz clock output to the sys-
tem.
This allows other devices to use the reference clock from the
DP83849C without requiring additional clock sources.
If the system does not require the CLK2MAC signal, the
CLK2MAC output should be disabled via the CLK2MAC disable
strap.
1.4 LED Interface
The DP83849C supports three configurable LED pins. The
LEDs support two operational modes which are selected
by the LED mode strap and a third operational mode which
is register configurable. The definitions for the LEDs for
each mode are detailed below. Since the LEDs are also
used as strap options, the polarity of the LED output is
dependent on whether the pin is pulled up or down.
Signal Name
LED_LINK_A
LED_LINK_B
LED_SPEED_A
LED_SPEED_B
LED_ACT/LED_COL_A
LED_ACT/LED_COL_B
Type
I/O
I/O
I/O
Pin #
19
43
20
42
21
41
Description
LINK LED: In Mode 1, this pin indicates the status of the LINK.
The LED will be ON when Link is good.
LINK/ACT LED: In Mode 2 and Mode 3, this pin indicates transmit
and receive activity in addition to the status of the Link. The LED
will be ON when Link is good. It will blink when the transmitter or
receiver is active.
SPEED LED: The LED is ON when device is in 100 Mb/s and OFF
when in 10 Mb/s. Functionality of this LED is independent of mode
selected.
ACTIVITY LED: In Mode 1, this pin is the Activity LED which is
ON when activity is present on either Transmit or Receive.
COLLISION/DUPLEX LED: In Mode 2, this pin by default indi-
cates Collision detection. For Mode 3, this LED output may be
programmed to indicate Full-duplex status instead of Collision.
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