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2. 8. Controls and Indicators
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Reset Button
The general hardware reset signal of CCU and VME–Bus can be initiated
by pushing the ”Reset Button”. It stays active for about 80 milliseconds.
Activity LED’s
The 4 digit LED–Display forms a hexadecimal coded value with MSB at the left side. Lighting re-
flects a logical ”One”.
The display shows the 4 bit contents of the Status–Register (see Figure 6: ) written on D7–D4 if this
value is less than 8, usually after power–up or reset.
If the MSB is set in the Status–Register the lower 3 digits from right to left reflect the activities of
the Ethernet–DMA, the CPU access to DRAM and the activity of the CPU on VME bus.
The intention is that after power–up or reset a basic test procedure changes the LED value at success
in steps from zero up to eight where eight means all tests have been passed and the monitor is run-
ning.
Fast Ethernet Status LED’s
The status information is available on the LED outputs pins of the DP83840.
LED1 Transmit activity, DP83840 pin 42
LED2 Receive activity, DP83840 pin 41
LED3 Good Link Status, DP83840 pin 38
LED4 Collision, DP83840 pin 36
”Collision ” ON indicates the occurrence of collisions in 10BASE–T or
100BASE–TX operation.
”Good Link Status” ON indicates valid link on the network connection and ready
state for normal operation.
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