On Tue, Feb 9, 2010 at 7:41 PM, PeterH <[email protected]> wrote: > > On Feb 9, 2010, at 4:23 PM, Gregg Eshelman wrote: > >> The later production IIfx don't need the special "black" external >> terminator. Some people with earlier versions have been able to stack two >> passive terminators and get it to work. > > A standard terminator applies a pair of 220 ohm pull-ups, and a pair of 330 > ohm pull-downs. > > As each such terminator applies a 100 ohm termination, and a pair of them > would apply a 50 ohm termination, and the characteristic impedance of the > line is more like 133 ohms, applying two conventional terminators is simply > BAD practice as the drivers within the Mac, and the drivers within the > device are capable of sinking only 48 milliamperes, and a 50 ohm termination > would require those devices to sink nearly 100 milliamperes ... a tenth of > an amp. > > I have never had an issue with IIfx terminators. > > Even unterminated buses have, and do work for me. > > Just my luck, I guess.
Why don't we solve this problem permanently? Terminators are electrically simple, and it should be very easy to reverse-engineer the IIfx terminator with a multi-meter. Anyone up for the job? I'd do it, but I don't have a IIfx (not from lack of wanting one!). - Alex -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/
