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Xref: sserve comp.sys.ibm.pc.hardware.chips:17192 comp.sys.ibm.pc.hardware.comm:6692 comp.os.386bsd.misc:5153 Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!yarrina.connect.com.au!wraith.internode.com.au!tipellium.apanix.apana.org.au!usenet From: miff@apanix.apana.org.au (Michael Smith) Newsgroups: comp.sys.ibm.pc.hardware.chips,comp.sys.ibm.pc.hardware.comm,comp.os.386bsd.misc Subject: Re: Re-clocking a 16550 for 230,400? Date: 1 Feb 1995 04:14:39 GMT Organization: Apanix Public Access Unix, +61 8 373 5485 (5 lines) Lines: 30 Message-ID: <3gn1rf$k3e@tipellium.apana.org.au> References: <3g8agg$19h@brasil.moneng.mei.com> <3ga99c$ms3@kaiwan.kaiwan.com> <3gbk6f$2tt@brasil.moneng.mei.com> NNTP-Posting-Host: seldon.apanix.apana.org.au jgreco@brasil.moneng.mei.com (Joe Greco) writes: >:You're right it will work (provided the support chips can take it, but >:230k shouldn't be a problem). But the problem will be all of your >:existing software will not work correctly due to the serial divisors >:will be off by a factor of two. If you're doing your own program or have >:a program which you can enter the divisors.. no prob... (Or just know >:that your term entry of 115.2k is really 230.4k.) >I hacked up a pair of STB DSP/550 cards early yesterday, we had the 3.6864 >MHz crystals in the lab but not the 7.3728 MHz crystals, so I only doubled >the clock. :-) They seem to work fine. FWIW, the currently-shipping NS16550D parts are capable of being clocked at up to 24MHz (check the datasheet 8) These are usually what you get if you buy 'real' 16550's (as opposed to, say the eXar parts). If you want standard baudrates, 4x is your best bet, or 14.7456MHz. You can probably get away with a 14.31818MHz crystal off an old PC motherboard for this - that's only 2.9% off the required clockrate, or 1/5 of a bit per byte. The clock recovery in most UARTs is more than capable of handling that. As for the support logic... *laugh* Unless someone is using 4000-series CMOS, or RTL perhaps on your card, you should have no problems at all. >Joe Greco - The Data Capture Fellow (and UNIX/Network Hacker) 414/362-3617 -- # mike smith : miff@apanix.apana.org.au - Silicon grease monkey # # "The question 'why are the fundamental laws of nature mathematical' # # then invites the trivial response 'because we define as fundamental # # those laws which are mathematical'". Paul Davies, _The_Mind_of_God_. #