1. Introduction
This document described the local controller software for LDSS-2. The software in question is written in FORTH, and runs on a 6809-based 4MS system.
LDSS-2 has six mechanisms under the control of or monitored by the 4MS:
The Aperture Wheel
The Filter Wheel
The Grism Wheel
The Camera Focus
The Doors
The Shutter
2.1 Aperture Wheel
The aperture wheel consists of a carosel with eight holes in it. It is controlled by a stepper motor (driven by an SMDM). The wheel is monitored by an incremental rotary encoder, and when stationary is held in position by means of a clamp. The clamp is operated pneumatically by means of a solenoid valve, and sensors exist to detect whether it is in the clamped or unclamped position.
2.2 Filter Wheel
For the purposes of the software, the filter wheel is identical to the aperture wheel.
2.3 Grism Wheel
For the purposes of the software, the grism wheel is identical to the aperture wheel, except that it has 6 holes.
2.4 Camera Focus
The camera focus can be driven over a range of approximately 750um by a stepper motor (driven by an SMDM), via a lead screw. The focus position is monitored by an SLVC (super-linear variable capacitor).
2.5 Doors
LDSS-2 has two access doors, which must be closed and locked during exposures, but which may need to be opened from time to time in order to change aperture masks, filters etc. They are opened/closed manually, but locked/unlocked pneumatically. A single solenoid valve controls both door locks. Each door has sensors to indicate whether the door is locked, and whether it is locked. Note that it is possible for the lock to be in the locked position even though the door is in fact open.
2.6 Shutter
The shutter is not controlled by the 4MS, but instead by the CCD or IPCS controller as appropriate. All decisions relating to the shutter are taken by the hardware, but the 4MS does play a role in monitoring this process.
The 4MS control software can be loaded from disc by issuing the following commands:
9 LOAD 76 LOAD 77 LOAD
In normal operation, the software would be programmed into EPROM, in which case it should start automatically.
4. Memory Map
The I/O address map is as follows:
DC00 Serial Comms Card (ACM-3)
DC30 PIA Card (GESPIA-2A)
DC40 Incremental Encoder Card #3 (GESINC-1)
DC50 Incremental Encoder Card #2 (GESINC-1)
DC60 Incremental Encoder Card #l (GESINC-1)
DC70 ADC Card (Syntel ADC3)
Please refer to the relevent data sheet for descriptions of individual registers.