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From: uhclem@trsvax.UUCP
Newsgroups: comp.sys.tandy
Subject: Re: Model 4
Message-ID: <193300009@trsvax>
Date: Fri, 17-Apr-87 10:36:00 EST
Article-I.D.: trsvax.193300009
Posted: Fri Apr 17 10:36:00 1987
Date-Received: Tue, 21-Apr-87 01:28:00 EST
References: <863@wjvax.wjvax.UUCP>
Lines: 49
Nf-ID: #R:wjvax.wjvax.UUCP:863:trsvax:193300009:000:2290
Nf-From: trsvax.UUCP!uhclem    Apr 17 09:36:00 1987


"What's wrong?  Has the little 386 computer got another bug? Awwwwwww."

>    I was wondering if anyone was familiar with type-ahead feature on a
>Model 4. Does Model 4 have it? If so, how do I enable it.Does TRSDOS 6.2
>support it?

The hardware does not actually perform this function.  It is entirely
up to the operating system on the machine to create the illusion of
nice keyboard hardware that has type-ahead.  You know, never do or fix
in hardware what you can cover with software.	:-(

The actual hardware is nothing more than an 8 x 8 grid of switches.
Press one and a data bit is pulled low (later inverted) when a certain
address line goes high (also inverted).  That's why 4P's have such a
hefty cable to the keyboard.  It has at least 16 wires in there, plus
shield!

The LDOS 5.x and LS-DOS 6.3 (also TRSDOS 6.[012]) simply scan the
keyboard every 33.33 msec, and if they find anything, it is
shoved into a local queue, which in 6.2 & 6.3 is up in some leftover
bytes at the end of the video static RAM.  LDOS 5.x uses some space
allocated in the memory allocated by the *KI driver, if you use it.
The driver in ROM does not do typeahead.

Since the keyboard hardware does not provide us with a nice interrupt
or a scan code or anything, it must be polled frequently, and floppy
I/O, or programs that disable interrupts a lot cause type-ahead to
not work.  There are also some prima-dona programs like Superscriptsit
that scan the keyboard themselves, so they may not have a typeahead
that works as well or has the same number of scans per second, etc.

If you have used other operating systems (TRSDOS 1.x, CP/M+ from RS) you
may have noted that typeahead does not work there.  That is why.


<This information is provided by an individual and is not nor should be
 construed  as  being  provided  by  Radio  Shack or Tandy Corp.  Radio
 Shack/Tandy Corp has no obligation to support the information provided
 in  any  way.  If  those  guys  had listened to me,  they  would  have
 implemented  debounce  correctly, even  in  typeahead mode.  Oh well.>
						
						"Thank you, Uh Clem."
						Frank Durda IV
						@ <trsvax!uhclem>


"Now place you hands on the keyboard and say... 'I will not turn too
 many bits on in my 32-bit multiplies again.'  Repeat it 32 times."