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Re: Where on motherboard to detect VBL?

Subject: Re: Where on motherboard to detect VBL?
From: Jerry <awanderin@yahoo.ca>
Date: Mon, 24 Jan 2011 23:03:05 -0700
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rich12345 <aiiadict@gmail.com> writes:

> I'm looking to find VBL signal on the Apple IIe motherboard.  Can it
> be done?
>
> Could I detect it from the peripheral BUS?

You could calculate it from the AUX SLOT: VID3 AND VID4.  Those signals
are not on the regular slots.

The closest you're going to get to VBL on the motherboard is /WNDW from
pin 38 of the IOU chip, or pin 7 on the AUX SLOT.  This blanks video
output during HBLANK and VBLANK times.

That's my assessment of things from the IIe Tech Ref manual, pages 207
and 208, and a perusal of chapters 7 and 8 in Understanding the Apple IIe.

--
Jerry    awanderin at yahoo dot ca

References:
- Where on motherboard to detect VBL?
  - From: rich12345 <aiiadict@gmail.com>

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