pwb@newt.phys.unsw.OZ.AU (Paul W. Brooks) (04/19/91)
In article <1991Apr10.104737.9962@cc.newcastle.edu.au>, eepjm@cc.newcastle.edu.au writes: > > Background: on many IBM-AT clones, one has a "turbo" mode or something similar > to select the processor clock rate. On some such machines the switching is > obviously hard-wired since the only way to change the speed is with a > front-panel pushbutton. On many others, however, the speed can be changed > via the keyboard (using Ctrl/Alt/+ or something similar), which implies that > the speed can be changed by software. > > Question: how does one do this? Presumably by writing something to a port, > but which port and what is the code? > > (Yes, I know that the answer might be different for different clones, but > if I can find out the answer for at least one clone, that gives me a > starting point. And you never know, a de facto standard might have arisen.) > Well, according to the Hardware Manual for my NEC Powermate IV (a '286 AT clone) the speed selection is done with a CTRL-ALT-'+' combination as you describe. But internally, it sets a special bit in the Keyboard controller chip output, and is not accessable to the rest of the system The chip is an 8742 / 8042. What that does electrically to the motherboard is anyones guess. Best of Luck! through a 'normal' I/O port. Paul Brooks |Internet: pwb@newt.phys.unsw.edu.au Uni. of N.S.W. |If you have trouble sleeping, try lying on the end of Kensington NSW 2033| your bed. With a little luck you'll drop off. AUSTRALIA | - Mark Twain.