[duxuser] Re: HP keyboards
- From: Theresa Tasse <theresa.tasse@xxxxxxxxxxx>
- To: duxuser@xxxxxxxxxxxxx
- Date: Thu, 25 Mar 2004 13:10:42 -0500
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.
Steve Dresser wrote:
> Hi Susan,
>
> You're way ahead of me on this one. I just had difficulty believing that a
> manufacturer would sell the same model keyboard with two different chip
> sets. I should have remembered the "change without notice" disclaimer.
>
> Steve
>
> On Wednesday 3/24/04 14:17 Susan wrote:
> >Steve,
> >
> >We did try switching the keyboards. Those that wouldn't do 6-key entry
> >on one computer wouldn't do 6-key entry on another computer that had
> >a working keyboard originally. So in this case, I can say for certain it was
> >the keyboard itself.
> >
> >Susan
> >
> >
> >Steve Dresser wrote on 3/24/2004, 12:03 PM:
> >
> >Susan,
> >
> >Unless you substituted a working keyboard for a non-working one, you
> >really don't know for sure if the problem lies with the keyboard, or with the
> >keyboard driver in the machine where the keyboard didn't work correctly.
> >This question may have as much to do with software as it does with hardware.
> >
> >Steve
> >
> >
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>
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--
T. Tasse,
Braille Transcriber
Education Assistant
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