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From: ching@pepsi.amd.com (Mike Ching)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 8 mhz "turbo" mode problem
Message-ID: <27266@amdcad.AMD.COM>
Date: 15 Sep 89 03:54:09 GMT
References: <3578@blake.acs.washington.edu> <1989Sep13.150422.6926@jose.uucp>
Sender: news@amdcad.AMD.COM
Reply-To: ching@pepsi.AMD.COM (Mike Ching)
Organization: Advanced Micro Devices, Inc. Sunnyvale CA
Lines: 22

In article <1989Sep13.150422.6926@jose.uucp> jim@jose.uucp (Jim) writes:
 >Dale Lear writes:
 >> 8 mhz "turbo" mode problem
 >> 
 >> <stuff deleted>
 >> 
 >>      Just for the record; the mother board is a no-brand-name Taiwan 
 >> made job called a "TURBO-640", the CPU is an 8mhz rated NEC V20, the 
 >
 >I had a 8 mhz turbo xt motherboard.  It came with a standard 8 mhz 8088,
 >and I bought the 8 mhz v20 for it.  It generally worked fine except for 
 >ocasional problems (similar to the ones you mention) and then the 
 >problems were only in turbo mode.  I removed the v20 and put the 8088 back
 >in, and the problems disappeared.

The problem is that the 8088 uses a 33% duty cycle clock (clock source is
divided by three) and the V20 uses a 50% duty cycle clock. The 8088 clock
in the PC doesn't meet the worst case timing requirement for a V20 at the
same speed. You could try another V20 in hopes of getting a faster one or
use one spec'ed for a higher speed.

mike ching