1666 - Power Manager II: Can I use the RESETb pin on a POWR1014 or POWR1220 to reset other parts of my circuit?
The RESETb pin on an ispPAC-POWR1014 or ispPAC-POWR1220 is bidirectional (open drain with internal pull-up). Its primary function is to be used as an input so that one can reset the device after it has been powered up.
The secondary function of this pin is to allow multiple Power Manager devices to be able to synchronize startup by having all of their RESETb pins tied together. In this way, the last device to come out of power-on reset gates all of the others by holding the mutual RESETb node low.
As an output, this pin generates an active LOW output signal on device power-up, but only asserts this signal for ~100us. For many applications, this is far too short a time to generate a reliable reset, especially as power may not have stabilized to the other devices needing to be reset. For this reason Lattice strongly discourages customers from using this pin to generate resets to external devices (other than Power Managers running from the same power supply lines). If you want to use a Power Manager device to generate a reset, we recommend using one of the digital outputs for this purpose, and controlling its state through one or more LogiBuilder instructions in PAC-Designer.