Digital Equipment DECstation 5000/100 Series, Maintenance Manual

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<7:0> LEDS
These bits determine the on/off state of the diagnostic LEDs.
When a register bit is 0, the corresponding LED is on. When a
register bit is 1, the corresponding LED is off. Since the LEDs
bits are automatically cleared at power up or reset, all the
LEDs are initially on.
Note:
The relationship between the state of these register bits and
the on/off state of the LEDs is the opposite of the LED error codes
represented in Table 4-1 in Chapter 4 and Table D-33 in Appendix D.
In the cited tables, the on state is represented by 1 and the off state is
represented by 0. Remember that the cited tables have nothing to do
with the register bits.
The correspondence between these register bits and the
diagnostic LEDs is not one to one right to left. Table E-9
lists the LED controlled by each register bit. The LEDs are
numbered 0 to 7 right to left when viewed from the rear.
Table E-9. LEDs Controlled by SSR LEDS Register Bits
Bit LED Controlled
0 3
1 2
2 1
3 0
4 7
5 6
6 5
7 4
E–20 CPU and System Registers