Datasheet
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5.0 Reset Operation
The DP83843 can be reset either by hardware or software.
A hardware reset may be accomplished either by asserting
the RESET pin during normal operation, or upon powering
up the device. A software reset is accomplished by setting
the reset bit in the Basic Mode Control Register.
While either the hardware or software reset can be imple-
mented at any time after device initialization, providing a
hardware reset, as described in Section 6.2 must be
implemented upon device power-up/initialization.
Omitting the hardware reset operation during the
device power-up/initialization sequence can result in
improper device operation.
Depending on the crystal starting up time, it is recom-
mended to wait 20 ms after the supply has reached its
proper value before initiating a hardware reset.
5.1 Power-up / Reset
When V
CC
is first applied to the DP83843 it takes some
amount of time for power to actually reach the nominal 5V
potential. This initial power-up time can be referred to as a
V
CC
ramp when V
CC
is “ramping” from 0V to 5V. When the
initial V
CC
ramp reaches approximately 4V, the DP83843
begins an internal reset operation which must be allowed
sufficient time, relative to the assertion and deassertion of
the RESET pin, to reset the device. There are two methods
for guaranteeing successful reset upon device power-up.
The first method accounts for those designs that utilize a
special power up circuit which, through hardware, will
assert the RESET pin upon power-up. In this case, the
deassertion (falling edge) of the RESET pin must not occur
until at least 500 µs after the time at which the V
CC
ramp
initially reached the 4V point.
The second method accounts for those applications which
produce a reset pulse sometime after the initial power-up of
the device. In this case, it is recommended that a positive
pulse, with a duration of at least 1 µs, be applied to the
RESET pin no sooner than 500 µs after the point in time
where the initial V
CC
ramp reached 4V.
In both methods described above, it is important to note
that the logic levels present at each of the hardware config-
uration pins of the DP83843 (see list below) are also
latched into the device as a function of the reset operation
(either hardware or software). These hardware configura-
tion values are guaranteed to be latched into the DP83843
2 µs after the deassertion of the RESET pin.
The hardware configuration values latched into the
DP83843 during the reset operation are dependent on the
logic levels present at the device pins shown in Table 4
upon power-up.
During the power-up/ reset operation the
LED1 through
LED5 pins are undefined, the SPEED10 will be asserted.
The 25 MHz clock reference must be applied for reset to
take effect.
5.2 Hardware Reset
A hardware reset is accomplished by applying a positive
pulse (TTL level), with a duration of at least 1 µs, to the
RESET pin of the DP83843 during normal operation. This
will reset the device such that all registers will be reset to
default values and the hardware configuration values will
be re-latched into the device (similar to the power-up/reset
operation).
5.3 Software Reset
A software reset is accomplished by setting the reset bit (bit
15) of the Basic Mode Control register (address 00h). This
bit is self clearing and, when set, will return a value of “1”
until the software reset operation has completed. The
period from the point in time when the reset bit is set to the
point in time when software reset has concluded is approx-
imately 5 µs.
The software reset will reset the device such that all regis-
ters will be reset to default values and the hardware config-
uration values will be re-latched into the device (similar to
the power-up/reset operation). Driver code should wait 500
µs following a software reset before allowing further serial
MII operations with the DP83843.
Table 4. Latched pins at Reset
Pin # Primary Function Latched in at Reset
21 COL
FXEN
22 CRS SYMBOL
38 LED_FDPOL PHYAD4
39 LED_LINK PHYAD3
40 LED_RX PHYAD2
41 LED_TX PHYAD1
42 LED_COL PHYAD0
63 THIN REPEATER
69
SERIAL10 SERIAL10