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Originally Posted by torsti76
Usually, it is needed with original drives as well. For DF1+, a well-behaved READY signal is mandatory. That's what the latch circuit provides.
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No, the latch (usually a 7474 flip flop) is there so that the motor can be controlled for each mechanism separately. There is only one internal and one external motor signal shared with each drive. When the external drive's select and motor are on at the same time, the latch remembers this and leaves the motor running until the drive is selected without the motor signal on the next time.
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If your drive issues a correct READY signal, it's sufficient to set the DS1 jumper to have ONE external drive. For more drives, you need the daisy-chain id switching which is usually coupled with the latch circuit anyway.
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No, the READY signal generated by the drive mechanism is for after the motor has been started and is up to speed.
The external drive case's circuitry provides a ready pulse for drive type/presence identification. This shares the same pin (READY) on the bus, but it is used for a different thing. The pulse is usually provided by a 7438 NAND chip and there is a specific algorithm for pulsing SELECT and MOTOR to read the ID pulse [1].
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On the big boxes, there's a jumper DF1: on/off. If set to on, this activates the DF1 latch circuit which, for the big boxes, is part of the mainboard.
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Looking at the A2000 schematics [2], the jumper connects the ready pulse from the 7438 NAND chip to the floppy bus, the 7474 motor latch for the internal df1 is always connected to the internal drive motor signal at the floppy bus, but this doesn't hurt anything.
[1]http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node01AB.html
[2]https://www.amigawiki.org/dnl/schematics/A2000_R6.pdf page 11