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. -- ----- 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/
