[duxuser] Re: Question about Keyboards
- From: Connie.Sullivan@xxxxxxxxxxx
- To: duxuser@xxxxxxxxxxxxx
- Date: Thu, 29 Apr 2004 11:20:37 -0500
This is a test. New spam software has been installed on our system and I
have been informed that I might not be able to reply to listserve messages.
-----Original Message-----
From: Theresa Tasse [mailto:theresa.tasse@xxxxxxxxxxx]
Sent: Wednesday, April 28, 2004 1:55 PM
To: duxuser@xxxxxxxxxxxxx
Subject: [duxuser] Re: Question about Keyboards
Let me set the record straight. Please fwd this on to anyone who could use
this info. How to tell if your keyboard is OK If you do not have Braille2000
or other translation software on your computer, start up a simple word
processing program such as "Wordpad". Put an empty document window on the
screen, so that if you type on the keyboard the text shows on the screen.
Then press the keys SDF JKL all at the same time and note what appears on
the screen. A "good-for-braille" keyboard will generate six letters on the
screen:
sdfjkl but not necessarily in precisely that sequence. For each time you
press all six keys at once, you should see six new letters appear on the
screen, one each of s d f j k 1, in any order. If you get this behavior,
your keyboard will be good for braille entry. A typical failing keyboard
generates only three or four letters rather than all six. Such a keyboard
will be OK for typing, but it is useless for braille entry. If you already
have Braille software on your computer, start Braille software, get a new
work area, and then try to enter a full cell (all dots). If your edition of
Braille2000 supports both the braille view and the print view, click the "B"
button to get the braille view before you enter braille cells. If you can
braille full cells time after time, your keyboard is just fine. If instead
of a full cell you get a single cell with just a few dots, your keyboard is
not acceptable for braille entry. If you get multiple cells, check to make
sure your keyboard settings do not use the "Time-dependent operation" (click
Adjust and then Keyboard to check on this). Please feel free to contact
Computer Application Specialties Company for assistance in evaluating the
keyboard of a computer you are considering for use with Braille2000. You can
reach us via the inquiry page. How to solve your keyboard Problem You are
not alone if you unpack your lovely new PC and discover that its keyboard
does not do well with six-key braille input. We estimate that more than half
of the keyboards that come with name-brand computer systems today do not do
well. See the background information below to learn how this is so, if you
are interested.
There are three basic paths to a solution:
1. Arrange for your computer vendor to provide an alternative keyboard, one
that
conforms to the "original IBM PC specification". You will have to explain to
the
vendor what an "original IBM PC specification " keyboard is. Refer them to
this web page and ask them for an "IBM PC down/up encoded keyboard with
n-key rollover". This phrase concisely describes the original IBM PC
keyboard characteristics. Tell them you really need 6-key rollover for the
keys SDFJKL. They may have a keyboard that will be OK, even though it is not
n-key rollover. 2. Visit second-hand computer stores and look for a
compatible older keyboard--older models tend more to be built to the
"original IBM PC specification". 3. Buy a new replacement keyboard. Computer
and office supply stores sell keyboards. Today, most of the keyboards do not
conform to the "original IBM PC specification" and are thus useless for
braille entry, so be sure to test the keyboards before buying. There are
some manufacturers still producing the kind of keyboard you want, but you
have to hunt for them. Computer Application Specialties Company stocks
affordable replacement keyboards that are guaranteed to handle six-key
braille inputs. When buying a replacement keyboard, be aware that there are
three types of keyboards differentiated by the size and shape of the
connector used to plug into the computer: The PC/AT type of keyboard
attaches with a large (about 5/8") round connector with 5 pins. The PS/2
type of keyboard attaches with a small (about 5/16") round connector with 6
pins. The USB type of keyboard attaches with a rectangular connector. Of
these three types, the PC/AT and PS/2 types are electronically identical and
differ only in the size of the connector. You can buy an adapter to convert
one round plug type to the other. The USB type of keyboard is electronically
different from the others. Although the USB type is the most modern, the
PS/2 type still is commonly used on new computer systems. If your keyboard
problem is on your laptop computer, it is not economically feasible to
replace the integral laptop keyboard. You can however attach an auxiliary
keyboard (to most laptop models). Check the laptop specifications to
determine what type of keyboard you can attach (usually either PS/2 or USB)
and then acquire a keyboard of that type that also handles six-key braille
inputs. Technological Background Information Prior to the IBM PC (early
'80s), keyboards generated character codes when you pressed a key. For
example, if you pressed the "A" key the code for "a" was generated. If you
pressed that same key while holding down the "Shift" key, the generated code
would be for "A" instead. The point is that the digital output of
old keyboards was character codes and the effects of the shift key were
handled inside the keyboard and caused different letter codes to be
produced. IBM changed the way keyboards behave by specifying that the IBM PC
keyboard would be "down/up" encoded with all keys treated equally. On this
type of keyboard, every key generates a digital "down" message when the key
is pressed and a digital "up" message when the key is released. All the keys
have assigned key-numbers. The operating system handles the keyboard
messages and thereby knows the state (down
or up) for every key. The IBM PC specification also provided that all keys
would
behave the same regardless of the current state of the keyboard. This means
that
if you have already pressed some combination of keys, any new key you press
or release still generates the normal "down" and "up" messages. This ability
to respond to newly-pressed keys regardless of how many keys are currently
held down is called "n-key rollover". In the IBM PC keyboard design, "Shift"
and "Ctrl" and "Alt" and even "Caps Lock"
are keys treated exactly the same way: when pressed, a "down" message is
generated and when released, an "up" message is generated. The meaning of
the key is determined only inside the operating system (DOS or Windows). The
operating system knows which standard key-number is the "Shift" key and when
you press "Shift" with "A", the operating system receives the two "down"
messages in sequence and knows
that the "A" is pressed while "Shift" is also down, and it then translates
the key-number for the "A" key not to "a" but to "A". This design was
necessary to support international keyboards in which the keytops would
differ both in layout
and in the symbols represented--one keyboard paradigm would thus handle all
international usage with just different software in the operating system. A
clever design, introduced in the early '80s with the advent of the IBM PC.
Given the "down/up" nature of the IBM PC keyboard, six-key braille entry is
a
snap: a program, such as Braille2000 merely has to listen to the "down" and
"up"
messages and to interpret clusters of "down" messages (for the key-numbers
for the SDF JKL keys) as cells. This original IBM PC specification behavior
has been disrupted in the last ten years by non-IBM-standard keyboards with
internal circuitry (a controller chip) that tracks only three or four key
presses at a time, having merely 3-key rollover. This kind of internal
keyboard logic simply cannot sense more than three or so keys pressed
simultaneously. And because of that, when you press more keys, only three or
four "down" messages (and later, three or four "up" messages) are sent out
to the computer. Some of the keys are missed, and thus some of the braille
dots are not there. The response of this kind of keyboard is fundamentally
insufficient to encode the six-key input. This limitation is part of the
internal logic of the keyboard and can be manifest on all types of
keyboards, including the new USB keyboards. The irony of the "new
technology" is that it does not significantly reduce the cost of the
keyboard. The original IBM PC keyboard design specification is not overly
expensive. It is true that contact-type keyboards use a matrix of key
switches and that to achieve n-key rollover those designs need an anti-ghost
diode per switch. Such diodes cost about 8 cents each (times 105 keys) plus
some added
manufacturing complexity. There are also non-contact keyboard types, using
resistive or capacitive keys and hall-effect sensors. These designs can be
n-key
rollover capable without using diodes.
By the way the key switch matrix is laid out, diode-free contact-type
designs can offer multi-key rollover for certain combinations of keys,
provided that the controller chip is prepared to track more than 3 keys
being "down". The "good for braille" keyboards of today are mostly of this
latter design: they are not true n-key rollover keyboards (because they lack
anti-ghost features and do not track
all possible patters of key presses) but the controller is prepared to
respond to multiple keys being "down" and the keys SDFJKL are distributed in
the matrix so that ghosting is not a problem for combinations of those keys.
The effect is 6-key rollover for SDFJKL, a perfect response for six-key
braille input. (The ideal keyboard also has the spacebar key on the matrix
where it does not conflict with
SDFJKL, thereby giving it 7-key rollover for SDFJKL and the spacebar.) With
USB keyboards, there is a new issue related to the buffering of the data
stream and the burden of managing the USB protocol. Some USB keyboards that
can sense patterns of SDFJKL may still fail to be satisfactory because the
multiple "down" and/or "up" messages that need to be sent out won't fit into
the data buffer (data packet overflow) and are lost. Or there may be times
when the USB controller is busy with protocol and does not have time to
sense all of the keys. The result is a USB keyboard that works nicely for
isolated cells (even SDFJKL pressed all at once) but which fails when there
is a continuing stream of such cells, as when brailling rapidly. It is most
likely that the inferior keyboard designs come about from the ignorance of
the importance of rollover--the inferior design is adequate for ordinary
typing input and it is doubtful that manufacturers (in Malaysia, Singapore,
and China) are aware of any software applications (such as Braille2000) that
need multiple-key response, beyond three keys. And to make matters worse,
the U.S. computer integrators (Dell, Compaq, Gateway, and others) do not
specify IBM PC behavior on their OEM bids for keyboard production.
Regardless of the technical issues (per-key diodes vs. capacitive vs.
hall-effect vs. buffer-length design factors), high volume production of
n-key rollover keyboards would be affordable, as were the keyboards made for
years by IBM for the original IBM PC. Thus, some keyboard designs remain
true to the original IBM PC standard (and are
by that design great for braille entry) while others, though not with n-key
rollover are quire satisfactory for six-key inputs, while the majority it
seems,
are not satisfactory at all. And only the original manufacturer knows
whether a given keyboard model has a rollover characteristic that is good
for braille. Such a specification is almost never published. For the end
user, only empirical testing will tell you for sure.
Deborah Barnes wrote:
> I know this information has been shared on list but at the time I
> didn't need it and now I do and I have a volunteer here so can't go
> searching. So I'm hoping some kind soul will send me the answer.
>
> I have some volunteers who will be using PerkyDucks. Can you tell me
> again how I know when a keyboard will do direct entry? Can I go into
> Word and try out the keyboard or do I have to be in Duxbury?
>
> Thanks bunches,
>
> Deb B.
>
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--
T. Tasse,
Braille Transcriber
Education Assistant
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