Why does the Apple ][ have a hardware-encoded keyboard?

From: Max Eskin <maxeskin_at_hotmail.com>
Date: Sat May 30 14:43:22 1998

I had just read the interview oyu mention yesterday. Could someone
give me some idea of what chips were involved in this thing? Did it
use PROMs, microcontrollers, or what? How can you make a game with
44 chips (not an expression of disbelief)?
>> It's reasonably obvious from looking at the design of all Apple ][
>> machines and their peripherals that they were designed to use the
>> simplest hardware possible. Things like the 'minimalist' disk
>> the bit-banger serial port and the Apple ][ I/O structure support
>> Why therefore did all Apple ][s use a hardware encoded keyboard with
>> fairly complex (and expensive) encoder IC? Software scanning would
>> been simpler in the hardware, not added much to the software, and
>> have been more versatile in many ways (the single-wire shift key mod
>> wouldn't have been necessary).
>At the time (mid-70's), surplus keyboards with ASCII encoded parallel
>outputs were readily available from many sources. Check, for example,
>the ads in the back of a '75 or '76 _Radio-Electronics_, or see
>many of the articles in the early _BYTE_'s. According to interviews
>with Wozniak (for example, _BYTE 1984:12 p.167), it was no big
>deal to find such a keyboard, put the right plug on the end, and
>plug it in (he says, of the Apple I, "You also had
>to get a keyboard and wire it into a 16-pin DIP connector".)
>Apple II motherboards were also available without a case or keyboard
>or power supply, and many hobbyists bought these as a way of saving
>a couple of bucks.
>Why use an encoder IC? Yes, it is cheaper if you skip this and
>have the CPU scan the keyboard. But encoder IC's weren't expensive
>at the time, and were an extremely common industry-standard
>solution; see, for example, Don Lancaster's _TTL Cookbook_ to get
>an idea at how readily available such encoders were in the mid-70's.
>Wozniak often did go for non-industry-standard solutions to
>peripheral interfacing, but generally only when it reduced the
>chip count. It seems to me that the encoder-IC approach to a
>keyboard has a lower part count than if you use SSI TTL IC's to let
>the CPU scan the keyboard.
>Chip count was an extremely important thing to Wozniak; for example,
>in the same interview I referenced before, he says
>"Nolan Bushnell
>was really annoyed because all their new games were coming out at 150-
>170 chips. He wanted low chip counts to reduce costs,
>and he had seen a version of Pong that I had done, that only used
>about 30 chips. He appreciated that. So he said if we could design
>a hardware Breakout in under 50 chips, we'd get 700 bucks; and if
>it was under 40 chips, we'd get $1000. ... We gave them a working
>breadboard for it. My first design was 42 chips. By the
>time we got it working it was 44, but we were so tired we
>couldn't cut it down. So we only got 700 bucks for
>Tim. (shoppa_at_triumf.ca)

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Received on Sat May 30 1998 - 14:43:22 BST

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