FDS RAM adaptor cable pinout

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 ███  1   3   5   7   9   B   ███
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 ███  2   4   6   8   A   C   ███
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Open-end view of the RAM adaptor's disk drive connector.


pin #   	*2C33 pin	*RAM pins	signal description
-----   	---------	---------	------------------
1		50		5 (green)	(O) -write
2		64		C (cyan)	(O) VCC (+5VDC)
3		49		6 (blue)	(O) -scan media
4		32		1 (brown)	(O) VEE (ground)
5		52		3 (orange)	(O) write data
6		37		B (pink)	(I) motor on/battery good
7		47		8 (grey)	(I) -writable media
8		-		-       	(I) motor power (note 1)
9		51		4 (yellow)	(I) read  data
A		45		A (black)	(I) -media set
B		46		9 (white)	(I) -ready
C		48		7 (violet)	(O) -stop motor

notes on symbols
----------------
(O):	Signal output.
(I):	Signal input.
- :	Indicates a signal which is active on a low (0) condition.
* :	These are corresponding pinouts for the 2C33 I/O chip, and the other  end  
of the RAM adaptor cable, which both are located inside the RAM adaptor.
1 :	The RAM adaptor does not use this signal (there is no wire in the cable 
to carry the signal). An electronically controlled 5-volt power supply 
inside the disk drive unit generates the power that appears here. This power 
is also shared with the drive's internal electric motor. Therefore, the 
motor only comes on when there is voltage on this pin.


(O) -write
----------
While active, this signal indicates that data appearing on the "write data" 
signal pin is to be written to the storage media.

(O) write data
--------------
This is the serial data the RAM adaptor issues to be written to the storage 
media on the "-write" condition.

(O) -scan media
---------------
While inactive, this instructs the storage media pointer to be reset (and 
stay reset) at the beginning of the media. When active, the media pointer is 
to be advanced at a constant rate, and data progressively transferred 
to/from the media (via the media pointer).

(O) -stop motor
---------------
Applicable mostly to the FDS disk drive unit only, the falling edge of this 
signal would instruct the drive to stop the current scan of the disk. 

(I) motor on/battery good
-------------------------
Applicable mostly to the FDS disk drive unit only, after the RAM adaptor 
issues a "-scan media" signal, it will check the status of this input to see 
if the disk drive motor has turned on. If this input is found to be 
inactive, the RAM adaptor interprets this as the disk drive's batteries 
having failed. Essentially, this signal's operation is identical to the 
above mentioned "motor power" signal, except that this is a TTL signal 
version of it.

(I) -writable media
-------------------
When active, this signal indicates to the RAM adaptor that the current media 
is not write protected.

(I) read data
-------------
when "-scan media" is active, data that is progressively read off the 
storage media (via the media pointer) is expected to appear here.

(I) -media set
--------------
When active, this signal indicates the presence of valid storage media.

(I) -ready
----------
Applicable mostly to the FDS disk drive unit only, the falling edge of this 
signal would indicate to the RAM adaptor that the disk drive has 
acknowledged the "-scan media" signal, and the disk drive head is currently 
at the beginning of the disk (most outer track). While this signal remains 
active, this indicates that the disk head is advancing across the disk's 
surface, and apropriate data can be transferred to/from the disk. This 
signal would then go inactive if the head advances to the end of the disk 
(most inner track), or the "-scan media" signal goes inactive.