7800 Multiframe Manual
7825DSK2-LG(-HD)(-3G) 3G/HD/SD Dual Downstream Keyer
INSTALLATION
Revision 2.0
Page 2-9
Devices on the Ethernet network continually monitor the receive data path for activity as a means of
checking that the link is working correctly. When the network is idle, the devices also send a link test
signal to one another to verify link integrity. The downstream keyer rear panel is fitted with two LEDs
to monitor the Ethernet connection.
10/100:
This LED is ON when a 100Base-TX link is last detected. The LED is OFF when a
10Base-T link is last detected. Upon power-up the LED is OFF as the last detected rate is
not known and therefore defaults to the 10Base-T state until rate detection is completed.
LN/ACT:
This dual purpose Green LED indicates that the 7825DSK2-LG(-HD)(-3G) has established
a valid linkage to its hub, and it determines whether the 7825DSK2-LG(-HD)(-3G) is
sending or receiving data. This LED will be ON when the 7825DSK2-LG(-HD)(-3G) has
established a good link to its supporting hub. This gives you a good indication that the
segment is wired correctly. The LED will BLINK when the 7825DSK2-LG(-HD)(-3G) is
sending or receiving data. The LED will be OFF if there is no valid connection.
2.8. CONNECTING THE GENERAL PURPOSE INPUTS AND OUTPUTS
Figure 2-2 shows a simplified schematic diagram of the GPIO circuitry. The user can connect
GP+3.3V supplied from the keyer unit into the Vext pin to provide power to the GPIO opto-isolator
circuitry. In this configuration the user can activate GPIs simply by connecting the GPI input pins to
Ground (see Figure 2-3). This can be done with a button, switch, relay or an open collector transistor.
In this configuration the GPOs will be internally pulled up to 3.3 volts (see Figure 2-5). 3.3 volts is
available to the user to be used for driving external circuitry. Care must be taken to limit the load to
0.5W ensuring that there is no affect on the power supply source on the unit.
Warning: Do not connect GP+3.3V from one unit to another unit’s GP+3.3V
output.
Alternately, the user can connect an external power source for the opto-isolator circuitry. The Vext
voltage must be greater than the voltage supplied to GPI by at least 3v. Figure 2-4 and Figure 2-6
show how to wire the GPIs and GPOs from an external power supply.
The tally outputs are active low with an internal pull up (10k Ohm) resistor to the Vext pin. When
active, the output will go low and is able to sink up to 10mA. When inactive, the signal will go high (to
the voltage applied to the Vext pin). Do not attempt to source more than 100
µ
A from the output.
