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Programmable Hardware Manual (PHM)
© Tibbo Technology Inc.
The SG and SR lines are used to control two status LEDs found on Tibbo products.
These LEDs can show various flashing patterns indicating the current device state
(see
). On the EM500, there is an added twist: the same pair of status
LEDs also indicates the current Ethernet link status through LED brightness. We
refer to the EM500's status LEDs as "dual-function LEDs." This is a patented
featured available exclusively on our MiniMo (R) devices. Here is how this works:
When a "live" Ethernet cable is not plugged into the RJ45 jack, flashing patterns
displayed by the status LEDs are "dimmed". That is, LEDs turn on at around 20% of
their nominal brightness. When a "live" Ethernet cable is plugged into the RJ45 jack,
flashing patterns are displayed at full brightness.
This dual functionality was designed into the EM500 for an important reason: Many
popular RJ45 jacks have two internal LEDs. With the EM500, it is possible to use
these LEDs both for the module state indication, and for Ethernet link indication.
This eliminates the need for any additional LEDs.
The third LED control line -- SE -- is a separate line for Ethernet link indication. The
SE LED will be on when the Ethernet interface is in the linked state.
There is no indication of the Ethernet link speed on the EM500. That is, there is no
LED control line to indicate whether the link is established in the 10BaseT or
100BaseT mode. Many networked devices have such an LED, but its existence has
become meaningless: it is actually very difficult to find any old-style 10Mb Ethernet
equipment in active use these days.
4.5.1.5
Power, Reset, and Mode Selection Lines
The EM500 should be powered from a stabilized DC power supply with a nominal
output voltage of 3.3V (+/- 5% tolerance). The module's current consumption is
approximately 260mA. Providing an adequate power supply is very important -- a
poorly built circuit may affect the EM500's operation. We recommend that you use a
switching power supply. One example of such a circuit is shown below.
For revision -00 devices, proper external reset is a must! Reset pulse should be
active LOW. We strongly advise against using low-cost RC circuits and other
unreliable methods of generating reset pulses. Reset should be applied for as long as
the power supply voltage is below 2.9V. We recommend using a dedicated reset IC,
such as the MCP130-300 device from Microchip. This part has a trip point at ~2.95V
-- perfect for the EM500.
Revision -01 modules have the reset IC onboard and do not rely on the external
reset. A master reset input is still provided.