I am aware of some problems with poorly sequenced devices that would fail over time from the constant abuse. Mixing ttl logic with opencollector devices was still a neat idea to keep a mininum chip count about the time those monitors were designed. During powerup ttl devices were trying to push a 1 onto a buss where several opencollector devices trying to pull the buss to ground at the same time. A lot of things happen in those first clock cycles on powerup, before everything falls into sync. The other Bob On Mon, 1 Oct 2007 06:40:00 -0700 (GMT-07:00), Steve Thatcher wrote: other output drive is attempting to use the data bus. The ROM output drivers may well fail after repeatedly being abused like this.