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From: george@wombat.bungi.COM (George Scolaro)
Newsgroups: comp.sys.nsc.32k
Subject: Re: pc532's r3 and r7
Message-ID: <9006120805.AA09154@wombat.bungi.COM>
Date: 12 Jun 90 15:05:31 GMT
Sender: news@daver.bungi.com
Lines: 29
Approved: news@daver.bungi.com

[In the message entitled "pc532's r3 and r7" on Jun 11, 20:29, Jon Buller writes:]
> 
> Can someone tell me what the value of r3 and r7 should be?  They are
> claimed to be clock termination resistors in the docs, but no value is
								????
> given for them.  If there is no "use this value and be quiet" answer,
> is there a way to easily figure it out?  Steve's kit has them as 220 and 330
> ohms, but I don't know which is which.  (The process of elimination can
> only take one so far...)

Actually, there are 4 resistors for termination, 2 x 220 and 2 x 330, one
220 and one 330 for each clock line (BCLK, /BCLK). The PCB only has the
holes for the 330 resistors. The 220 resistors have to be soldered to the
back of the board.  The doc explains how to do it in the CPU SECTION first
paragraph:

	for each clock line {
		330 ohm resistor from clock to ground (holes provided)
		220 ohm resistor from clock to +5V (holes not provided)
	}

This terminates the clock traces at close to the PCB impedance and reduces
reflections from the end of the trace.

best regards,

-- 
George Scolaro
george@wombat.bungi.com                [37 20 51 N / 122 03 07 W]