[HN Gopher] The Apple II Circuit Description (1983)
___________________________________________________________________
The Apple II Circuit Description (1983)
Author : bookofjoe
Score : 48 points
Date : 2023-11-02 14:58 UTC (2 days ago)
(HTM) web link (archive.org)
(TXT) w3m dump (archive.org)
| dark_star wrote:
| Wow. Good to see this here. At age 17, having an Apple ][+ and
| this book got me started on the path to being an electronics
| engineer.
| mcwiggin2 wrote:
| Can you imagine if documentation like this was available for
| modern hardware?!
|
| Even something "open" like the raspberry pi doesn't have this
| level of detail available. The process of deep but accessible
| technical documentation appears to be a lost art.
| joezydeco wrote:
| You're just using the wrong part. If you get an STM32 or NXP
| iMX, there are tens of thousands of pages of TRM available to
| describe the function of every block inside the SoC. The core
| iMX7 technical document is over 7,000 pages.
|
| You won't get everything, especially anything ARM has licensed
| out to the chipmakers like the CPU/NVIC/AHB, but it's a lot
| deeper than you probably need.
| ajross wrote:
| FWIW, while this is a reasonably good book (though stay away from
| the Disk section, IIRC it completely misunderstands the way the
| Apple encoding works), consensus is that "Understanding the Apple
| II", by Jim Sather, is the clearly best work on the subject:
| https://archive.org/details/understanding_the_apple_ii
| retrac wrote:
| Most of the components in the original Apple II are still
| manufactured. The character ROM is hard to find. The 16 kilobit
| DRAMs are definitely obsolete, but not exactly rare (dozens of
| millions were manufactured). Since it's mostly 7400 LS TTL logic
| you can easily substitute a different circuit to replace a
| missing part, use modern EEPROMs, etc. (Beware of subtle timing
| issues - you can't always swap a modern CMOS part for a TTL
| part.)
|
| Accordingly, you can still build an Apple II today:
| https://www.reactivemicro.com/product/apple-ii-rev-0/ Same store
| also sells a complete kit for an Apple II+ including components,
| as well as assembled. (Never bought from them, can give no
| review.)
|
| The Apple II may be one of the last computers so-thoroughly
| documented. Your 1970s era TI databooks for 74xx TTL components
| will give you a complete transistor-level schematic of the logic.
| And the 6502 itself has been completely reverse-engineered. So
| it's possible to know where every transistor in the computer is
| and what it does. And the machine is just about simple enough,
| one person can fit it all in their head, mostly.
| DonHopkins wrote:
| Mysterious Orange Line -- Before leaving the subject of HIRES, we
| must discuss the "Mysterious Orange (or Pink) Line." This
| vertical line appears from time to time along the left edge of
| the screen (Reference 8.2). The phenomenon is rooted in the
| hardware. Notice in Fig. 8-28* that when the video is shifted one
| clock cycle by A11-9, 70 nS of garbage is shifted such that it
| falls within the unblanked portion of the screen (point Z). This
| unwanted half-dot ends up in the video output at point AA (the
| left edge of the screen).
|
| Can we determine where this dot comes from and what its value is?
| It comes from bit 6 of the memory location that maps to the video
| address just to the left of the left-most byte displayed on the
| screen. If bit 6 of this critical location is set, and if bit 7
| of the left-most byte is set, then there will be a half-dot at
| the left edge of the screen (see the last signal plotted in Fig.
| 8-29). The phase of this dot is such that it will be pinkish-
| orange in color. The critical addresses themselves can be
| determined from Fig. 5-8*. They are all within the 16K HIRES
| page. Of these locations, 128 are legitimate screen locations
| along the right edge of the screen. The remaining 64 are unused
| locations. The mapping is indicated in Fig. 8-30. You can see the
| Mysterious Line by running the following 20 second program.
| 10 REM MYSTERIOUS ORANGE LINE 20 POKE --16297,0 30
| POKE --16304,0 40 POKE --16302,0 100 P = 8192
| 110 FOR I = P TO P + P 120 POKE 1,128 : NEXT I 130
| FOR N = 0 TO 7168 STEP 1024 140 FOR I = 127 + P + N TO 1023
| + P + N STEP 128 150 POKE 1,64 : NEXT I 160 FOR I = 39 + P
| + N TO 935 + P + N STEP 128 170 POKE 1,64 : NEXT I 180 FOR
| I = 79 + P + N TO 975 + P + N STEP 128 190 POKE 1,64 : NEXT I
| 200 NEXT N 999 END
|
| Fig. 8-30. Mysterious orange line.
|
| MYSTERIOUS ORANGE LINE
|
| UNUSED MEMORY LOCATIONS STORE THE TOP THIRD OF THE MYSTERIOUS
| LINE.
|
| LEGITIMATE SCREEN LOCATIONS ON THE RIGHT STORE THE BOTTOM TWO-
| THIRDS OF THE MYSTERIOUS LINE.
| user3939382 wrote:
| I have an Apple IIc in good condition. Love that thing. It turned
| me into a programmer in early childhood.
___________________________________________________________________
(page generated 2023-11-04 23:00 UTC)