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Apple IIgs technical questions
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Anthony Ortiz
2017-07-25 22:46:05 UTC
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What is the best Apple IIgs technical manual out there that would be equivalent to Sathers' "Understanding the Apple IIe"?

I'm interesting in understanding why the IIgs doesn't support the cycle-sensitive graphics demos (eg. French Touch); is it due to the new RGB display? Or perhaps vapor-lock no longer works because the bus no longer leaks stray capacitance? Or perhaps something is off with the Mega II chip?

Also, does the IIgs have its own specific quirks that could be exploited such as the vapor lock on the IIe or is it no longer timing-sensitive as the prior II models were? That is, if you were to write an emulator for the IIgs and you were *not* worried about backwards compatibility with prior-model Apple II software and only concerned with IIgs software, would you still have to worry about cycle-accuracy and clock phases/timings?
cb meeks
2017-07-26 17:35:28 UTC
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Post by Anthony Ortiz
Also, does the IIgs have its own specific quirks that could be exploited such as the vapor lock on the IIe
Uh, what is the vapor lock on the IIe? I haven't heard that one before but sounds cool. :-)
David Schmidt
2017-07-26 18:37:14 UTC
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Post by cb meeks
Post by Anthony Ortiz
Also, does the IIgs have its own specific quirks that could be exploited such as the vapor lock on the IIe
Uh, what is the vapor lock on the IIe? I haven't heard that one before but sounds cool. :-)
Here's a good treatment from Nick W.:
https://groups.google.com/d/msg/comp.sys.apple2/UK0x1JMNjNg/F94M7Sg3AQAJ
Anthony Ortiz
2017-10-16 01:38:12 UTC
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Post by Anthony Ortiz
What is the best Apple IIgs technical manual out there that would be equivalent to Sathers' "Understanding the Apple IIe"?
I'm interesting in understanding why the IIgs doesn't support the cycle-sensitive graphics demos (eg. French Touch); is it due to the new RGB display? Or perhaps vapor-lock no longer works because the bus no longer leaks stray capacitance? Or perhaps something is off with the Mega II chip?
Also, does the IIgs have its own specific quirks that could be exploited such as the vapor lock on the IIe or is it no longer timing-sensitive as the prior II models were? That is, if you were to write an emulator for the IIgs and you were *not* worried about backwards compatibility with prior-model Apple II software and only concerned with IIgs software, would you still have to worry about cycle-accuracy and clock phases/timings?
Still hoping for an answer to the best IIgs technical manual ah la Sathers. Anybuddy?
James Davis
2017-10-16 01:42:21 UTC
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Post by Anthony Ortiz
Post by Anthony Ortiz
What is the best Apple IIgs technical manual out there that would be equivalent to Sathers' "Understanding the Apple IIe"?
I'm interesting in understanding why the IIgs doesn't support the cycle-sensitive graphics demos (eg. French Touch); is it due to the new RGB display? Or perhaps vapor-lock no longer works because the bus no longer leaks stray capacitance? Or perhaps something is off with the Mega II chip?
Also, does the IIgs have its own specific quirks that could be exploited such as the vapor lock on the IIe or is it no longer timing-sensitive as the prior II models were? That is, if you were to write an emulator for the IIgs and you were *not* worried about backwards compatibility with prior-model Apple II software and only concerned with IIgs software, would you still have to worry about cycle-accuracy and clock phases/timings?
Still hoping for an answer to the best IIgs technical manual ah la Sathers. Anybuddy?
Have you tried Googling "Apple II Differences" ?! -- ANR
Anthony Ortiz
2017-10-16 01:45:37 UTC
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Post by James Davis
Post by Anthony Ortiz
Post by Anthony Ortiz
What is the best Apple IIgs technical manual out there that would be equivalent to Sathers' "Understanding the Apple IIe"?
I'm interesting in understanding why the IIgs doesn't support the cycle-sensitive graphics demos (eg. French Touch); is it due to the new RGB display? Or perhaps vapor-lock no longer works because the bus no longer leaks stray capacitance? Or perhaps something is off with the Mega II chip?
Also, does the IIgs have its own specific quirks that could be exploited such as the vapor lock on the IIe or is it no longer timing-sensitive as the prior II models were? That is, if you were to write an emulator for the IIgs and you were *not* worried about backwards compatibility with prior-model Apple II software and only concerned with IIgs software, would you still have to worry about cycle-accuracy and clock phases/timings?
Still hoping for an answer to the best IIgs technical manual ah la Sathers. Anybuddy?
Have you tried Googling "Apple II Differences" ?! -- ANR
That's too generic; some very specific and technical feats such as vaporlock would never be found by googling for "differences".
James Davis
2017-10-16 02:12:16 UTC
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Post by Anthony Ortiz
Post by James Davis
Post by Anthony Ortiz
Post by Anthony Ortiz
What is the best Apple IIgs technical manual out there that would be equivalent to Sathers' "Understanding the Apple IIe"?
I'm interesting in understanding why the IIgs doesn't support the cycle-sensitive graphics demos (eg. French Touch); is it due to the new RGB display? Or perhaps vapor-lock no longer works because the bus no longer leaks stray capacitance? Or perhaps something is off with the Mega II chip?
Also, does the IIgs have its own specific quirks that could be exploited such as the vapor lock on the IIe or is it no longer timing-sensitive as the prior II models were? That is, if you were to write an emulator for the IIgs and you were *not* worried about backwards compatibility with prior-model Apple II software and only concerned with IIgs software, would you still have to worry about cycle-accuracy and clock phases/timings?
Still hoping for an answer to the best IIgs technical manual ah la Sathers. Anybuddy?
Have you tried Googling "Apple II Differences" ?! -- ANR
That's too generic; some very specific and technical feats such as vaporlock would never be found by googling for "differences".
I posted a list of GS manuals in another thread:

https://groups.google.com/forum/#!starred/comp.sys.apple2/JdC6A3BJ1UU

Apple usually has a "Differences Appendix" in their TRMs. You could look in and search their AIIGS TRMs/PDFs.
Michael J. Mahon
2017-10-16 07:15:59 UTC
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Post by Anthony Ortiz
Post by Anthony Ortiz
What is the best Apple IIgs technical manual out there that would be
equivalent to Sathers' "Understanding the Apple IIe"?
I'm interesting in understanding why the IIgs doesn't support the
cycle-sensitive graphics demos (eg. French Touch); is it due to the new
RGB display? Or perhaps vapor-lock no longer works because the bus no
longer leaks stray capacitance? Or perhaps something is off with the Mega II chip?
Also, does the IIgs have its own specific quirks that could be exploited
such as the vapor lock on the IIe or is it no longer timing-sensitive as
the prior II models were? That is, if you were to write an emulator for
the IIgs and you were *not* worried about backwards compatibility with
prior-model Apple II software and only concerned with IIgs software,
would you still have to worry about cycle-accuracy and clock phases/timings?
Still hoping for an answer to the best IIgs technical manual ah la Sathers. Anybuddy?
I'm not aware of any comparable hardware exegesis of the IIgs.

However, the floating bus applications are not the result of the bus
"leaking stray capacitance".

Any bus has capacitance from its lines to ground, as does any wire. The bus
wires are a little longer than a typical wire, and any connected IC or card
adds somewhat to that capacitance.

The critical thing that makes it possible to read the last state of the
data bus is that reading an IO address that *does not drive* the bus
results in the processor picking up the last state driven onto the bus--in
this case, on the previous half-cycle. This state is available because
nothing else has driven the bus, and its previous state is still present
because of the bus's unavoidable capacitance.
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
John Brooks
2017-10-16 08:52:37 UTC
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Post by Michael J. Mahon
Post by Anthony Ortiz
Post by Anthony Ortiz
What is the best Apple IIgs technical manual out there that would be
equivalent to Sathers' "Understanding the Apple IIe"?
I'm interesting in understanding why the IIgs doesn't support the
cycle-sensitive graphics demos (eg. French Touch); is it due to the new
RGB display? Or perhaps vapor-lock no longer works because the bus no
longer leaks stray capacitance? Or perhaps something is off with the Mega II chip?
Also, does the IIgs have its own specific quirks that could be exploited
such as the vapor lock on the IIe or is it no longer timing-sensitive as
the prior II models were? That is, if you were to write an emulator for
the IIgs and you were *not* worried about backwards compatibility with
prior-model Apple II software and only concerned with IIgs software,
would you still have to worry about cycle-accuracy and clock phases/timings?
Still hoping for an answer to the best IIgs technical manual ah la Sathers. Anybuddy?
I'm not aware of any comparable hardware exegesis of the IIgs.
However, the floating bus applications are not the result of the bus
"leaking stray capacitance".
Any bus has capacitance from its lines to ground, as does any wire. The bus
wires are a little longer than a typical wire, and any connected IC or card
adds somewhat to that capacitance.
The critical thing that makes it possible to read the last state of the
data bus is that reading an IO address that *does not drive* the bus
results in the processor picking up the last state driven onto the bus--in
this case, on the previous half-cycle. This state is available because
nothing else has driven the bus, and its previous state is still present
because of the bus's unavoidable capacitance.
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
Reading the floating bus video fetch may not work on the GS because the 65816 drives the data bus every clock cycle by multiplexing the upper 8-bit 'bank' of the 24-bit address bus onto the data bus.

-JB
@JBrooksBSI
John Brooks
2017-10-16 04:28:27 UTC
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Post by Anthony Ortiz
What is the best Apple IIgs technical manual out there that would be equivalent to Sathers' "Understanding the Apple IIe"?
I'm interesting in understanding why the IIgs doesn't support the cycle-sensitive graphics demos (eg. French Touch); is it due to the new RGB display? Or perhaps vapor-lock no longer works because the bus no longer leaks stray capacitance? Or perhaps something is off with the Mega II chip?
Also, does the IIgs have its own specific quirks that could be exploited such as the vapor lock on the IIe or is it no longer timing-sensitive as the prior II models were? That is, if you were to write an emulator for the IIgs and you were *not* worried about backwards compatibility with prior-model Apple II software and only concerned with IIgs software, would you still have to worry about cycle-accuracy and clock phases/timings?
I'm interesting in understanding why the IIgs doesn't support the cycle-sensitive graphics demos (eg. French Touch); is it due to the new RGB display? Or perhaps vapor-lock no longer works because the bus no longer leaks stray capacitance? Or perhaps something is off with the Mega II chip?
I haven't looked into French Touch demo compatibility. As far as i know, the Mega II chip allows floating-bus reads of the phase 1 video bus fetch from Mega II I/O registers, same as earlier Apple II models.
Post by Anthony Ortiz
Also, does the IIgs have its own specific quirks that could be exploited such as the vapor lock on the IIe or is it no longer timing-sensitive as the prior II models were? That is, if you were to write an emulator for the IIgs and you were *not* worried about backwards compatibility with prior-model Apple II software and only concerned with IIgs software, would you still have to worry about cycle-accuracy and clock phases/timings?
A few items here:

1) Yes, the GS is still cycle-accurate with regard to clock phases/timings.

2) 40col, gr, & hgr all do 40 bus reads every scan line (40 of 65 cycles), but 80 col, dgr, dhgr perform 80 reads every 40 cycles, so only half of the video fetches can be viewed on the floating bus. Similarly, SHR does 160 bitmap reads every 40 cycles (plus a SCB read and 32 palette bytes), so about 1/4 of those video fetches can be observed.

3) The phase 1 frame buffer fetch is either 'owned' by the Mega II for 14MHz //e modes, or by the VGC for 16MHz SHR modes. Switching quickly between M2 & SHR will cause artifacts as the bus fetch pipelines of each chip flushes & refills.

4) There are major differences between the look of //e NTSC graphics and GS composite-out graphics for hgr, dhgr, etc. The GS calculates all colors as 444 RGB (partially-faking NTSC along the way) and then converts that RGB to NTSC using a converter chip rather than bit-banging the NTSC signal directly like prior Apple II composite video systems. Look at the title screen for Bard's Tale on a //e & a GS to see what I mean.

In my experience, the best references are the Apple hardware reference manual, schematics, and performing tests on the GS hardware. Asking here is good too.

-JB
@JBrooksBSI
Tom Porter
2017-10-16 12:47:34 UTC
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I am not a GS guy, but I have some information pertaining to Incompatibility of GS vrs an II(E)-line for instance..

When one uses 1bit audio and attempts to play it ... in most instances 1mhz mode comes out apx 60-65% speed of original designed for IIE... and on 2.8mhz mode apx 130% speed...

I had to adjust my 'music' drivers to check to see if its an IIGS before issuing a new command (for music setup or sound effect setup) and adjust the playback speed modifier byte.
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