jeff@nmtvax.nmt.edu (- Jeff -) (12/05/89)
This is probably a useless question, but there is a mysterious key on my
XT-keyboard called the 'Sys Req' key. I've seen this key on many other
IBM and compatible keyboards and I am just curious if anyone knows what it
is for and how to access it? I can't seem to find anything in my DOS 3.3
manual about it. Anyone know what this key is for? Just curious...
- Jeff -
jeff@nmtvax.nmt.edu
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+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++kds10773@uxa.cso.uiuc.edu (Ken S.) (12/06/89)
The SysReq key can be polled using entry point 0x85 of int 0x15 (system services), however I believe that's only implemented on AT's, so on your XT keyboard, it's most likely useless. I'm afraid I also don't know of any less technical ways to access it. - Ken Stillson
Ralf.Brown@B.GP.CS.CMU.EDU (12/06/89)
In article <1989Dec5.181045.10621@ux1.cso.uiuc.edu>, kds10773@uxa.cso.uiuc.edu (Ken S.) wrote: >The SysReq key can be polled using entry point 0x85 of int 0x15 (system >services), however I believe that's only implemented on AT's, so on your >XT keyboard, it's most likely useless. I'm afraid I also don't know >of any less technical ways to access it. You can't poll SysRq that way, since the BIOS *calls* INT 15/AH=85h whenever the SysRq key is pressed or released. If you want to get SysRq, you have to hook INT 15 and check for AH=85h. INT 15 - OS HOOK - SYSTEM REQUEST KEY PRESSED (AT,XT2,XT286,CONV,PS) AH = 85h AL = 00h press = 01h release Return: CF set on error AH = status Note: called by keyboard decode routine SeeAlso: INT 09 -- UUCP: {ucbvax,harvard}!cs.cmu.edu!ralf -=-=-=-=- Voice: (412) 268-3053 (school) ARPA: ralf@cs.cmu.edu BIT: ralf%cs.cmu.edu@CMUCCVMA FIDO: Ralf Brown 1:129/46 FAX: available on request Disclaimer? I claimed something? "How to Prove It" by Dana Angluin 13. proof by reference to inaccessible literature: The author cites a simple corollary of a theorem to be found in a privately circulated memoir of the Slovenian Philological Society, 1883.
cs4g6ag@maccs.dcss.mcmaster.ca (Stephen M. Dunn) (12/08/89)
In article <189@nmtvax.nmt.edu> jeff@nmtvax.nmt.edu (- Jeff -) writes:
$This is probably a useless question, but there is a mysterious key on my
$XT-keyboard called the 'Sys Req' key. I've seen this key on many other
$IBM and compatible keyboards and I am just curious if anyone knows what it
$is for and how to access it? I can't seem to find anything in my DOS 3.3
$manual about it. Anyone know what this key is for? Just curious...
SysReq is short for "System Request", and is a key introduced with the
AT. I don't think there's a way to read it on an XT, as the function you
call is part of the AT's BIOS extensions.
The use of this key is up to an application (actually, it was designed
with operating system uses in mind). Writers of an operating system that
runs several tasks but only allows one to have control of the screen,
for example, might use it to allow the user to switch between displaying
the screen of one task and the screen of another task.
Basically, you can use it for whatever you want, but it isn't read like
the other keys through standard keyboard read functions.
--
Stephen M. Dunn cs4g6ag@maccs.dcss.mcmaster.ca
<std_disclaimer.h> = "\nI'm only an undergraduate!!!\n";
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If it's true that love is only a game//Well, then I can play pretenddarcy@druid.uucp (D'Arcy J.M. Cain) (12/08/89)
In article <189@nmtvax.nmt.edu> jeff@nmtvax.nmt.edu (- Jeff -) writes: >This is probably a useless question, but there is a mysterious key on my >XT-keyboard called the 'Sys Req' key. I've seen this key on many other >IBM and compatible keyboards and I am just curious if anyone knows what it >is for and how to access it? I can't seem to find anything in my DOS 3.3 >manual about it. Anyone know what this key is for? Just curious... > > - Jeff - > jeff@nmtvax.nmt.edu This key can not be read by normal keyboard reads. To use this key you must intercept int 15h and test for ah=85h. If not pass through to the old int 15h. If so the look at al. If it is 0 then the SysReq key has just been pressed. If 1 the it has just been released. I used this one to turn a Hercules graphics screen into a negative of itself. There aren't many programs that make use of this key. I suspect that that is because it is only available on AT's. -- D'Arcy J.M. Cain (darcy@druid) | "You mean druid wasn't taken yet???" D'Arcy Cain Consulting | - Everybody - West Hill, Ontario, Canada | No disclaimers. I agree with me |
darcy@druid.uucp (D'Arcy J.M. Cain) (12/08/89)
In article <1989Dec5.181045.10621@ux1.cso.uiuc.edu> kds10773@uxa.cso.uiuc.edu (Ken S.) writes: >The SysReq key can be polled using entry point 0x85 of int 0x15 (system Careful. You don't poll the SysReq key. See my response to the previous poster. The hardware actually makes the "call" to this entry point. The programmer is in the position of capturing that call. -- D'Arcy J.M. Cain (darcy@druid) | "You mean druid wasn't taken yet???" D'Arcy Cain Consulting | - Everybody - West Hill, Ontario, Canada | No disclaimers. I agree with me |
wei@hpctdls.HP.COM (Bill Ives) (12/09/89)
>/ hpctdls:comp.sys.ibm.pc / kds10773@uxa.cso.uiuc.edu (Ken S.) / 11:10 am Dec 5, 1989 / >The SysReq key can be polled using entry point 0x85 of int 0x15 (system >services), however I believe that's only implemented on AT's, so on your >XT keyboard, it's most likely useless. I'm afraid I also don't know >of any less technical ways to access it. > - Ken Stillson Ken is correct... this is the only standard way of accessing the sys req key. THe original poster also asked what it was used for -- since I have used it I may be able to fill in some details there. The sys req key was meant to activate the main tasker/controller in a multitasking system. It was theorised at least in the documentation I have, that a tasker ( for 286 systems which support multi-tasking) could hook into sys req and provide ( or use ) ABIOS routines which give tasks essentail functions in protected mode. The sys req key is ideal for activating a main tasker since the keyboard does not have to be polled for an asynchronous sys req to come through ( unlike control-break) . This would have been a good choice for OS/2's session manager shell ( the shell that doesn't include PM ), but alas they chose control-esc -- don't ask me why :-). My use of it was to put in a hardware debug register manager for the 386 that would work behind any application -- even if that application went into protected mode (i.e Smalltalk V/286). Thought you might be interested in its intended use - even if obscure. Bill Ives HP CTD