Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!yale!cmcl2!adm!smoke!gwyn From: gwyn@smoke.brl.mil (Doug Gwyn) Newsgroups: comp.sys.apple2 Subject: Re: ZIP GS... HOW FAST? Message-ID: <16371@smoke.brl.mil> Date: 10 Jun 91 03:24:03 GMT References: Organization: U.S. Army Ballistic Research Laboratory, APG, MD. Lines: 24 In article PKBRANDON@MSUS1.MSUS.EDU writes: >I believe that the InCider issue describing how to upgrade a TWGS to 13mz >was an *April* issue. 'Nuf said! Nope -- indeed some TWGS owners HAVE increased the speed of their CPUs to anywhere from 8 to 13MHz. The highest speed I've heard of that seems to be reliable is 10MHz. One can get 65816 chips from WDC, in SMALL quantities, that are certified for operation at high speeds; they come with a so-called Shmoo plot delineating the range of speed vs. applied Vcc. For speeds above 9MHz, you almost always have to crank up the DC power supply above the nominal 5V level, perhaps as high as 6V. This is not something to be done lightly, and it is best to sever the TWGS power traces from the rest of the IIGS and increase the voltage only for the TWGS, not the rest of the IIGS. Apart from possibly needing to jack up the voltage and install a CPU chip capable of faster operation, one needs to replace the crystal oscillator with one running at a higher rate (4x the CPU clock rate). At higher speeds, you may also have to replace the TWGS RAM with faster versions. I don't recommend performing such an upgrade, except possibly to as much as 9MHz with no adjustment of power supply voltage. (I.e. just two "chip" replacements.)