DP83620SQ Datasheet, PDF (38/105 Pages) Texas Instruments – DP83620 Industrial Temperature Single Port 10/100 Mbps Ethernet Physical Layer

DP83620
SNLS339C – JANUARY 2011 – REVISED APRIL 2013
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5.8 INTERNAL LOOPBACK
The DP83620 includes a Loopback Test mode for facilitating system diagnostics. The Loopback mode is
selected through bit 14 (Loopback) of the Basic Mode Control Register (BMCR). Writing 1 to this bit
enables MII transmit data to be routed to the MII receive outputs. Loopback status may be checked in bit 3
of the PHY Status Register (PHYSTS). While in Loopback mode the data will not be transmitted onto the
media. To ensure that the desired operating mode is maintained, Auto-Negotiation should be disabled
before selecting the Loopback mode.
5.9 POWER DOWN/INTERRUPT
The Power Down and Interrupt functions are multiplexed on pin 7 of the device. By default, this pin
functions as a power down input and the interrupt function is disabled. Setting bit 0 (INT_OE) of MICR
(11h) will configure the pin as an active low interrupt output.
5.9.1 Power Down Control Mode
The PWRDOWN/INTN pin can be asserted low to put the device in a Power Down mode. This is
equivalent to setting bit 11 (POWER DOWN) in the Basic Mode Control Register, BMCR (00h). An
external control signal can be used to drive the pin low, overcoming the weak internal pull-up resistor.
Alternatively, the device can be configured to initialize into a Power Down state by use of an external pull-
down resistor on the PWRDOWN/INTN pin. Since the device will still respond to management register
accesses, setting the INT_OE bit in the MICR register will disable the PWRDOWN/INTN input, allowing
the device to exit the Power Down state.
5.9.2 Interrupt Mechanisms
The interrupt function is controlled via register access. All interrupt sources are disabled by default. Setting
bit 1 (INTEN) of MICR (11h) will enable interrupts to be output, dependent on the interrupt mask set in the
lower byte of the MISR (12h). The PWRDOWN/INTN pin is asynchronously asserted low when an
interrupt condition occurs. The source of the interrupt can be determined by reading the upper byte of the
MISR. One or more bits in the MISR will be set, denoting all currently pending interrupts. Reading of the
MISR clears ALL pending interrupts.
Example: To generate an interrupt on a change of link status or on a change of energy detect power state,
the steps would be:
• Write 0003h to MICR to set INTEN and INT_OE
• Write 0060h to MISR to set ED_INT_EN and LINK_INT_EN
• Monitor PWRDOWN/INTN pin
When PWRDOWN/INTN pin asserts low, the user would read the MISR register to see if the ED_INT or
LINK_INT bits are set, i.e. which source caused the interrupt. After reading the MISR, the interrupt bits
should clear and the PWRDOWN/INTN pin will de-assert.
5.10 ENERGY DETECT MODE
When Energy Detect is enabled and there is no activity on the cable, the DP83620 will remain in a low
power mode while monitoring the transmission line. Activity on the line will cause the DP83620 to go
through a normal power up sequence. Regardless of cable activity, the DP83620 will occasionally wake
up the transmitter to put ED pulses on the line, but will otherwise draw as little power as possible. Energy
detect functionality is controlled via register Energy Detect Control (EDCR), address 1Dh.
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Configuration
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