Date   : Tue, 22 Aug 2000 20:53:26 -0700 (PDT)
From   : Angus Duggan <angus@...>
Subject: Re: Elite-A

Michael Foot writes:
>I found this timout problem with Elite-A on my emulator and pcBBC as well.
>It's a problem that's been hastling me for a while. Can anyone elaborate on
>what happens internally when this spin down happens? ie. what signals are
>passed from the 8271 to the other ICs to signal this?

Have a look at the Read Drive Status op of the 8271 (write &AC into the
command register); bit D6 and D2 are latching "drive ready" status bits (D6
not ready, D2 ready I think). The 8271 data sheet says:

* Note the two ready bits are zero latching.  Therefore, to clear the drive
  not ready condition, assuming the drive is ready, and to detect it via
  software, one must issue this command twice.

The drive head unload time is the top 5 bits of the third parameter to the
initialisation command (&35). The value is the number of disc revolutions
before the head is automatically unloaded. When the head is unloaded, the
drive ready status is cleared.

a.