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Programmable Hardware Manual (PHM)
© Tibbo Technology Inc.
Further information on status LEDs can be found in
4.7.1.5
Power, Reset, and Mode Selection Lines
The EM200 should be powered from a stabilized DC power supply with nominal
output voltage of 5V (+/- 5% tolerance). Current consumption of the EM200 is
approximately 220mA (in 100BaseT mode). Providing an adequate power supply is
very important -- poorly built circuit may affect EM200 operation. We recommend
that you use a switching power supply circuit. One (but not the only) example of
such circuit is shown below.
Proper external reset is a must! Reset pulse should be an active HIGH. We strongly
advise against using low-cost RC-networks and other unreliable methods of
generating reset pulse. Reset should be applied for as long as the power supply
voltage is below 4.6V. We recommend using a dedicated reset IC with brownout
detection, such as MAX810. Reset pulse length should be no less than 50ms,
counting from the moment the power supply voltage exceeds 4.6V.
If the EM200 is used to serve as a communications co-processor in a larger system
that has its own CPU it is also OK to control the RST line of the EM200 through a
general-purpose I/O pin of the "host" microcontroller. I/O pins of many
microcontrollers default to HIGH after the powerup and this means that proper reset
will be applied to the EM200 when the host device is switched on. All the host
microcontroller has to do is release the EM200 from reset at an appropriate time by
switching the state of the I/O line to LOW.
The function of the MD line is described in
.
Power supply circuit
Many power supply circuits will work well. The one below is being used by Tibbo.
The circuit can handle input voltages in the 9-30V range.