Filter Changer Control Rack Interface

'D' Connector Technical Specification

This control interface is implemented via 37 way 'D' connector located on the rear panel of the system box.

All signals are TTL logic level, implemented in 74HC(T) series CMOS chips, i.e. low = 0V, high = +5V. There are 8 inputs, 8 outputs and an additional 16 lines available to program the rotor speed using the built in frequency generator.

Pin Assignment

IDC Ribbon Connection	D Connector Pin Number	Signal Denomination
1	1	Request position (LSB)
2	20	Request position
3	2	Request position (MSB)
4	21	Goto
5	3	Spin/stop
6	22	Direction
7	4	Step (positive edge triggered)
8	23	Frequency
9	5	Current position (LSB)
10	24	Current position
11	6	Current position (MSB)
12	25	Ready
13	7	Stopped
14	26	Bus direction
15	8	Mclock
16	27	Rotor pulse
17	9	1 (Rotor speed (BCD 0 - 9))
18	28	2
19	10	4
20	29	8
21	11	1 (BCD 0 - 90)
22	30	2
23	12	4
24	31	8
25	13	1 (BCD 0 - 900)
26	32	2
27	14	4
28	33	8
29	15	Frequency range Low=0-999,High=0-99.9
30	34	Reserved
31	16	Reserved
32	35	Enable internal frequency Low=OFF
33	17	Ground
34	36	Ground
35	18	Ground
36	37	Ground
37	19	Ground

Input Descriptions (pins 1 - 8)

1-3. Request position
These lines encode the required position in binary format, such that 000 represents filter position 1, and 111 represents filter position 8. Requests to go to an invalid position (e.g. position 7 in a 6-filter rotor) will be treated as a request to go to the highest actual filter position. The rotor will go to the new position by the shortest available route. If the two routes are the same length, the rotor will go in the normal direction as defined below.

4. Goto (Positive edge triggered)
If this line goes high when the rotor is in discontinuous mode, the rotor will move to the position encoded on the request position lines. This line must go low and then high again to initiate another goto, and will only take effect if the ready line is high. A movement will also occur if the goto line is high when the ready line goes from low to high.

5. Spin/stop
Rotor will spin continuously at a speed determined by the frequency input if this line is low. It will enter stopped (discontinuous rotation) mode if this line is high.

6. Direction
When this line is low, the rotor will spin in the normal direction, i.e. from lower to higher filter positions. When it is high, the rotor will spin in the reverse direction. Normal rotation is clockwise when the rotor is viewed from the light source side.

7. Step (Positive edge triggered)
If this line goes high when the rotor is in discontinuous mode, the rotor will step to the next filter position. The step will be to the next higher position if the direction line is low (normal case), or to the next lower position if the direction is high. The ready line will immediately go low, and will remain low until the rotor has reached the next filter position. The step line must go low and then high again to initiate another step. A step will only take place if the ready signal is high in an analogous way to the goto signal.

8. Frequency
Rotor will synchronise to a control frequency applied to this input if the spin/stop line is low. The rotor will synchronise in phase such that the transition between the highest and lowest numbered filter positions (i.e. the midpoint between them) will coincide with the rising edge of the control wave form. The duty cycle of this is of no importance. Frequency can also be applied via the front panel socket on the system box. If no signal is applied to either input then speed will be determined by the internal frequency generator (programmed either from the front panel switches or from an external source, see later).

Output Descriptions (pins 9 - 16)

9 - 11. Current Position
These lines carry the current filter position in the same format as the request position inputs, and operate during both continuous and discontinuous modes. When a step or goto request is issued in discontinuous mode, these outputs immediately assume the value appropriate for the new filter position. They should therefore be read in conjunction with the ready line to determine when they become valid. A similar verification should be made when the rotor is spinning continuously.

12. Ready
This line will go high when the rotor is spinning continuously and is in phase with the control frequency as described above. It will also go high in discontinuous mode when the rotor has reached the new requested position. Thus it will temporarily go low if either a new speed or filter position is programmed, or during changes between continuous and discontinuous operation.

13. Stopped
When the spin/stop line goes high, the rotor will come to a halt at filter position 1. The stopped line will go high when this condition is achieved, and will remain high for as long as the spin/stop line is high. It serves to acknowledge that the rotor is now operating in discontinuous mode.

14. Bus direction *
As spin direction can be controlled from other sources, this line serves as an indicator as to the direction of spin. It is in the opposite phase to the set direction input i.e. it is high for rotation in the normal direction.

15. Mclock *
This signal is generated from an optical sensor at the edge of the rotor wheel. It is used internally for accurate positional information, and in the standard version of the rotor generates 24 pulses per revolution.

16. Rotor pulse *
This signal is derived from a sensor that detects a reference point on the rotor. Its low-to-high transition when the rotor is spinning continuously in the normal direction occurs midway between the lowest and highest filter positions (in the reverse direction, this point would represent the high-to-low transition). This signal is normally low and the pulse has a short duty cycle, which is of no practical significance.

*Not required for external control. Included for compatibility and system testing/polling operations and because they were there.

Setting rotor speed externally using the built in frequency generator.

Rotor speed can be set externally using a control frequency as described above. However provision has also been made to allow programmed selection in BCD format of an internally generated frequency. This facility occupies connector pins 17 - 32 as shown above.

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