Multiple-driver glitch in digital busses

Previous publications have described an effect termed “wired-OR glitch” on digital bus lines driven by multiple transmitters. This effect occurs when a given line is pulled to the active “low” state simultaneously by open collector/drain transmitters. If one of the transmitters switches to the inactive open-collector state, the line will momentarily be forced toward the high level, due to the propagation of the current transition, despite the other transmitter maintaining a constant low. Most prior work has focused on Futurebus handshake and control lines. It is shown that this effect can also be observed on data lines. Even if the two transistor´s “on” times never overlap. Measurements are provided for a TeleComBus-style system using (Backplane-Transceiver Logic) BTL devices. Simulations art used to provide a detailed analysis of the glitch effect, and show that this effect must be considered in any digital bus system using more than one, physically-separated transmitter