D Finnigan wrote:

Kelvin Sherlock wrote:

---
It's possible that everybody, including Apple, has been wrong for 37
years but extraordinary claims require extraordinary evidence.

I found articles going back to the 1986 release of the IIgs that described the Mega II as a "complete Apple II on a chip." Most likely someone made
an
assumption about the chip, and it spread around, was repeated, and stuck
for 37 years.

Never mind; more reading yields the answer. It came from Apple Computer, per the Cortland documentation that Kelvin Sherlock referred to in his previous article.

From page 27 of the Custom ICs document:

"The Mega II, shown in Figure 10, has virtually all the characteristics of
an Apple II on a chip; it supports a slotted architecture and has built-in peripherals."

-+-

But I think it got corrupted into "a complete Apple IIe on a chip," which definitely isn't correct.

--
]DF$
The New Apple II User's Guide:
https://macgui.com/newa2guide/

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Kelvin Sherlock wrote:

---
It's possible that everybody, including Apple, has been wrong for 37
years but extraordinary claims require extraordinary evidence.

I found articles going back to the 1986 release of the IIgs that described
the Mega II as a "complete Apple II on a chip." Most likely someone made an assumption about the chip, and it spread around, was repeated, and stuck for
37 years. This happens in every knowledge domain, not just with vintage computers.

Here's a post from September 1986 that asks if the Mega II is an emulator
chip:
https://macgui.com/usenet/?group=6&id=3010

Here's a reference to an October 1986 BYTE Magazine article about the Mega
II:
https://macgui.com/usenet/?group=1&id=3626


THE MEGA II
The Mega II is a custom CMOS chip containing about 3000 gates and a 2K-byte
by 8 ROM (for the character generator). It replaces the following chips from the Apple IIe and IIe: char­acter generator ROMs for eight lan­guages. several TTL chips that per­form logic functions. and the MMU (memory management unit). IOU (in­put/output unit). TMG (timing genera­tor). and GLU (general logic unit) custom chips.

In previous Apple II designs, the re­freshing of memory was tied directly to the Apple II video mode. The Mega II includes an 8-bit counter for
refresh­ing the 128K bytes of (slow) memory associated with the Apple
IIe/IIc model; it does five cycles of RAM refresh during the horizontal
retrace of each video scan line and refreshes the 128K bytes of memory in
3.25 milliseconds. By taking care of RAM refresh the Mega II chip opens the Apple II design to new video modes that were impossible before.

--
]DF$
The New Apple II User's Guide:
https://macgui.com/newa2guide/

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Mitchell Spector wrote:

D Finnigan <[email protected]> wrote:

From page 27 of the Custom ICs document:

"The Mega II, shown in Figure 10, has virtually all the characteristics of >>an Apple II on a chip; it supports a slotted architecture and has built-in >>peripherals."

-+-

But I think it got corrupted into "a complete Apple IIe on a chip," which >>definitely isn't correct.

The Mega II *is* a complete Apple IIe on a chip. It's just, for the
most
part, missing the CPU and ROM firmware.

We don't need to argue this further, but in my opinion, if you state that it
is missing the CPU and ROM firmware, then in my opinion you conclude that it
is not a complete Apple IIe on a chip.

:-)

The Mega II apparently just sits in the IIGS performing unrelated I/O tasks, NOT emulating an Apple IIe (the fact that it can, is wasted). A
part of it is used for providing classic Apple II text and video modes,
but
that may be it. Which again begs the question....if it isn't the Mega II, what logic allows the Apple IIGS to emulate an Apple IIe?

Part of the answer is the 8-bit mode in Mensch's 65C816, right?

--
]DF$
The New Apple II User's Guide:
https://macgui.com/newa2guide/

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In article <[email protected]>,
D Finnigan <[email protected]> wrote:

Kelvin Sherlock wrote:

---
It's possible that everybody, including Apple, has been wrong for 37
years but extraordinary claims require extraordinary evidence.

I found articles going back to the 1986 release of the IIgs that described >the Mega II as a "complete Apple II on a chip." Most likely someone made an >assumption about the chip, and it spread around, was repeated, and stuck for >37 years. This happens in every knowledge domain, not just with vintage >computers.

Here's a post from September 1986 that asks if the Mega II is an emulator >chip:
https://macgui.com/usenet/?group=6&id=3010

Here's a reference to an October 1986 BYTE Magazine article about the Mega >II:
https://macgui.com/usenet/?group=1&id=3626

THE MEGA II
The Mega II is a custom CMOS chip containing about 3000 gates and a 2K-byte >by 8 ROM (for the character generator). It replaces the following chips from >the Apple IIe and IIe: char­acter generator ROMs for eight lan­guages. >several TTL chips that per­form logic functions. and the MMU (memory >management unit). IOU (in­put/output unit). TMG (timing genera­tor). and GLU >(general logic unit) custom chips.

In previous Apple II designs, the re­freshing of memory was tied directly to >the Apple II video mode. The Mega II includes an 8-bit counter for >refresh­ing the 128K bytes of (slow) memory associated with the Apple >IIe/IIc model; it does five cycles of RAM refresh during the horizontal >retrace of each video scan line and refreshes the 128K bytes of memory in >3.25 milliseconds. By taking care of RAM refresh the Mega II chip opens the >Apple II design to new video modes that were impossible before.

I don't know the source of the above paragraph and what it's trying to say,
but I do not believe it is correct. The memory refresh of slow memory in a IIgs done by the Mega II is identical to how a //e does it. The //e had to make changes to the II+ logic since it supported 64kbit DRAMs (a II+ only supports 4kbit and 16kbit DRAMs), and these new big DRAMs require 8 bits of rows to be refreshed, but the IIgs uses the same 64kbit DRAMs so it's just
done the same way. There are differences in how SHR works, and maybe that's what they're trying to describe (as far as I know, the details of SHR
memory accesses and refresh are not fully documented, but note that simply showing the SHR screen fully refreshes memory just like all other video
modes on an Apple II). On an Apple II, it's the text and lores modes which have to do careful trickery to fully refresh memory in the required time
(and it's why the video memory layout is so weird). HGR and SHR could
easily refresh memory if they were linear--but HGR can be done with slight tweaks to text mode and need very little additional logic, and that's why
it is the way it is. SHR was a new mode done on a new chip where saving one TTL part didn't matter, so it's linear in memory.

Kent

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Kent Dickey wrote:

In article <[email protected]>,
D Finnigan <[email protected]> wrote:

Here's a reference to an October 1986 BYTE Magazine article about the Mega >>II:
https://macgui.com/usenet/?group=1&id=3626


THE MEGA II
The Mega II is a custom CMOS chip containing about 3000 gates and a
2K-byte
by 8 ROM (for the character generator). It replaces the following chips >>from
the Apple IIe and IIe: char­acter generator ROMs for eight lan­guages. >>several TTL chips that per­form logic functions. and the MMU (memory >>management unit). IOU (in­put/output unit). TMG (timing genera­tor). and
GLU
(general logic unit) custom chips.

In previous Apple II designs, the re­freshing of memory was tied directly >>to
the Apple II video mode. The Mega II includes an 8-bit counter for >>refresh­ing the 128K bytes of (slow) memory associated with the Apple >>IIe/IIc model; it does five cycles of RAM refresh during the horizontal >>retrace of each video scan line and refreshes the 128K bytes of memory in >>3.25 milliseconds. By taking care of RAM refresh the Mega II chip opens
the
Apple II design to new video modes that were impossible before.

I don't know the source of the above paragraph and what it's trying to
say,
but I do not believe it is correct.

The source is the October 1986 BYTE Magazine article by Gregg Williams,
senior technical editor at BYTE.

It's on page 86 of the issue of BYTE magazine dated October 1986.


--
]DF$
The New Apple II User's Guide:
https://macgui.com/newa2guide/

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In article <[email protected]>,
D Finnigan <[email protected]> wrote:

Kent Dickey wrote:

In article <[email protected]>,
D Finnigan <[email protected]> wrote:

[snip]

In previous Apple II designs, the re­freshing of memory was tied directly >>>to
the Apple II video mode. The Mega II includes an 8-bit counter for >>>refresh­ing the 128K bytes of (slow) memory associated with the Apple >>>IIe/IIc model; it does five cycles of RAM refresh during the horizontal >>>retrace of each video scan line and refreshes the 128K bytes of memory in >>>3.25 milliseconds. By taking care of RAM refresh the Mega II chip opens >>>the
Apple II design to new video modes that were impossible before.

I don't know the source of the above paragraph and what it's trying to
say,
but I do not believe it is correct.

The source is the October 1986 BYTE Magazine article by Gregg Williams, >senior technical editor at BYTE.

It's on page 86 of the issue of BYTE magazine dated October 1986.

--
]DF$
The New Apple II User's Guide:
https://macgui.com/newa2guide/

Sorry, I didn't mean to imply I doubted that BYTE magazine published those statements in 1986. I meant I'm not sure what his source was, but I believe
he is mistaken. He seems to have fumbled up the SHR being able to read
the SCB (one cycle) and palette data (read in 4 cycles) during HBL with a change to how refresh works.

Kent

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Kent Dickey wrote:

Sorry, I didn't mean to imply I doubted that BYTE magazine published those statements in 1986. I meant I'm not sure what his source was, but I
believe he is mistaken.

What was the author's source? Let's assume that Gregg Williams wrote his article in September 1986. Apart from his own direct investigation, how many sources were even available in September 1986? He could have asked some
Apple employees, but he also could have referred to the Cortland documents
or similar pre-release developer's documentation.

--
]DF$
The New Apple II User's Guide:
https://macgui.com/newa2guide/

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