Model 28 Synchronization Upgrade
	New Firmware: This page announces and describes a non-commercial offering of new firware for the Plan B Model 28 Tap Clock module. This new executable programs as firmware into the microcontroller heart of the module. Feature Summary: This new firmware, in combination with some form of input clock inversion, substantially increases the modules ability to synchronize with external clock inputs applied to the "phaselock" input. Additionally, a new output is provided which emits at 24 times the input signal. This new output allows for companion circuitry which could augment the frequency multiplication available from the panel face of the module. Availability: As a non-commercial offering, there is no charge for the executable itself. As this effort is not factory subsidized, a small cost incurs for the upgrade of an existing module or for provisioning of a new AT89C2051-24 microcontroller for user upgrade. Contact: North American owners should contact Big City Music for this upgrade, European owners can contact Tim Stinchcombe.

Note: Installation of this new firmware, into a Tap Clock module, will not by itself result in input clock synchronization. Signals input to an unmodified Tap Clock module's "Phaselock" input cannot possibly synchronize unless they are inverted. The graphic right depicts the logical inversion needed for input clock signals. This inversion might occur using an external module (inline to the Model 28 Phaselock input) or by the addition of a simple inverting circuit to the module itself.
	The Phaselock input is effective for signals that swing from zero to positive voltage levels. External modules that invert the direction (by 180 degrees) but maintain this signal swing will accomodate the Phaselock requirement. The Phaselock input is not effective for negative voltages. The image left, depicts how Modules described as Inverters can operate differently. Transforming positive voltages to negative voltages will not accomodate Phaselock input requirment.
As an alternative, Tim Stinchcombe has provided a design and method for implementing the required inversion with a simple modification requiring only part replacement. The design and the installation procedure can be referenced on this page. Note: Hardware modification of the Model 28 Tap Clock voids the factory warranty

New Feature This new firmware takes advantage of a 2 pin header on the PCB to provide the additional 24x output pulse. Before powering up the module a cosmetic inspection should be made to ensure this header is not shorted in any way. This header is behind the panel and not readily accessible. The figure left indicates the location for both the microcontroller which hosts the new firmware and the adjacent 2 pin header.