The signals in the altitude and azimuth subsystems are almost the same except the prefix "AL" or "AZ" respectively. Therefore, they are both described in this section. The signals are named as azimuth signals. They are divided into the following groups that indicate where the signals originate (inputs to the computer), or where they have to be routed (outputs from the computer):
The above abbreviations are used as the second prefix after the standard prefix AL and AZ for altitude and azimuth respectively.
| NAME | TYPE | DESCRIPTION |
| AZPACUR1 | AI*12 | PA current to motor 1 |
| AZPACUR2 | AI*12 | PA current to motor 2 |
| AZPACUR3 | AI*12 | PA current to motor 3 |
| AZPACUR4 | AI*12 | PA current to motor 4 |
In each motor unit, there are three temperature switches of 70 degrees Celsius and three of 90 degrees. All the motor temperature signals in this table are the 70 degrees Celsius switches.
The 90 degree switches are in the interlock chain. They generate the signal ILMOTOR; see Subsection 3.2.7 for more information.
| NAME | TYPE | DESCRIPTION | Terminal strip# |
| AZMTWIND1 | DI*1 | Motor 1, winding over-temperature | |
| AZMTBEAR1 | DI*1 | Motor 1, bearing over-temperature | |
| AZMTBRAK1 | DI*1 | Motor 1, brake winding over-temperature | |
| AZMTWIND2 | DI*1 | Motor 2, winding over-temperature | |
| AZMTBEAR2 | DI*1 | Motor 2, bearing over-temperature | |
| AZMTBRAK2 | DI*1 | Motor 2, brake winding over-temperature | |
| AZMTWIND3 | DI*1 | Motor 3, winding over-temperature | |
| AZMTBEAR3 | DI*1 | Motor 3, bearing over-temperature | |
| AZMTBRAK3 | DI*1 | Motor 3, brake winding over-temperature | |
| AZMTWIND4 | DI*1 | Motor 4, winding over-temperature | |
| AZMTBEAR4 | DI*1 | Motor 4, bearing over-temperature | |
| AZMTBRAK4 | DI*1 | Motor 4, brake winding over-temperature |
| NAME | TYPE | DESCRIPTION |
| AZPIVREF | AO*12 | Velocity reference to PI controller |
| AZPITORQUE | AO*12 | Torque reference to PI controller |
| AZPIVERR | AI*12 | Velocity error |
| AZPIACTV | AI*12 | Actual velocity (sum of four tacho signals) |
| AZPICREF | AI*12 | Net current ref. (without pre-tension for motors) |
| AZPIVRS8* | DO*1 | Velocity reference, 8 times greater sensitivity |
| AZPIATR* | DO*1 | Apply torque reference |
| AZPICVL* | DO*1 | Close velocity loop |
| AZPIAPT* | DO*1 | Apply pre-tension |
| AZPIRESET | DO*1 | Reset PI controller after interlock |
| SIGNAL | TYPE | DESCRIPTION |
| AEDATI | DO 1 | Pin 1 (bit 20) |
| AEDATI | DO 1 | Pin 2 (bit 21) |
| AEDATI | DO 1 | Pin 3 (bit 22) |
| AEDATI | DO 1 | Pin 4 (bit 23) |
| AEDATI | DO 1 | Pin 5 (bit 24) |
| AEDATI | DO 1 | Pin 6 (bit 25) |
| AEDATI | DO 1 | Pin 7 (bit 26) |
| AEPARI | DO 1 | Pin 8 (bit 27) - Parity bit |
The following signals indicate that the telescope is close to the interlock limits. The computer should stop the telescope in an orderly fashion. The signals do not imply any interlock at all. Interlock in hardware first takes place when the interlock limit switches are passed.
These signals are generated in AL only. The corresponding bits in the AZ are indicated as "Reserved" in the schematic diagrams and are connected to the negated logic level. In this way, the software can be the same.
| NAME | TYPE | DESCRIPTION |
| VSPOSLIMI* | DI*1 | Altitude 90 deg proximity limit switch (Upper limit=1) |
| VSNEGLIM* | DI*1 | Altitude 10 deg proximity limit switch (Lower Limit=1) |
The signals described in this subsection enables the computer to gather information about the interlock situation, or to issue commands to the interlock subsystem.
Some interlock signals are generated only in the AL system or only in the AZ system; the corresponding bits in the AZ or AL respectively is indicated on the hardware drawings as "Reserved" and are connected to the negated logic level. This has the advantage that the basic software for both AL and AZ can be the same.
If the emergency stop signal ILEMCOM is asserted, it indicates that any emergency stop button is pressed. Note that ILEMSTO shows that the emergency stop button on the AL or AZ power rack respectively has been pressed.
Interlock Signals for AL and AZ
| NAME | TYPE | DESCRIPTION |
| AZILENABLE* | DO*1 | Disengage brakes and enable amplifiers |
| AZILORIDE* | DO*1 | Override interl. (parallel with manual override) |
| AZIL380PF | DI*1 | 380V AC phase failure, amplifier disabled |
| AZILEMSTO | DI*1 | AZ emergency stop pushbutton; amplifier disabled |
| AZILEMCOM | DI*1 | Any! em. stop button pressed; amplifier disabled |
| AZILPI | DI*1 | Max. velocity exceeded; amplifier disabled |
| (generated by PI controller; reset via AZPIRESET) | ||
| AZILMOTOR | DI*1 | Overtemp (90 deg) of any of the four motors; amplifier disabled |
| AZILPADIS | DI*1 | Power amplifiers disabled; ie. any interlock active |
Interlock Signals for AL Only
| NAME | TYPE | DESCRIPTION |
| ALILLOCK | DI*1 | Locking device engaged; amplifier disabled |
| ALILPOSLIM* | DI*1 | Positive interlock limit signal; amplifier disabled |
| ALILNEGLIM* | DI*1 | Negative interlock limit signal; amplifier disabled |
| ALILBRMAN | DI*1 | Brakes manually disengaged; amplifier disabled |
Interlock Signals for AZ Only
| NAME | TYPE | DESCRIPTION |
| AZIL3D | DI*1 | 3 degree limit passed; amplifier disabled |
| AZILHB | DI*1 | Hydrostatic pressure low; amplifier disabled |
| NAME | TYPE | DESCRIPTION |
| WATCH DOG | DO 1 | Trigger output for alitude amplifiers watch-dog |
| AZSPAREx | DI*1 | Spare, x=1 through 3 |