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December 2013

posted Dec 8, 2013, 11:14 AM by Dan Antohi   [ updated Feb 1, 2014, 1:26 PM]
 
11 Dec 2013
 
    

    Although all ‘Interface 1bis’ units are thoroughly tested before beingshipped, there were complaints regarding the occasional corruption of theinterface’s operating system. As pointed out before, the extent to which thismay occur differs largely, depending on the state of the Spectrum's powersupply, both the external PSU and the internal voltage regulator circuits aswell as on the method of connecting / disconnecting the power: by inserting /removing the PSU’s plug from the Spectrum’s power socket or by using a switchmains socket.

    Because these factors can hardly be controlled, a method forquickly restoring the interface’s operating system, at the push of a button, wasdevised.

     Nevertheless, the problem remainedunder investigation, in order to find a permanent and reliable remedy, preferablysimple enough to be implemented by the users themselves. To this end, numerous testswere conducted with ‘problematic’ ‘Interface 1bis’ units, using different ZXSpectrum models, power supplies and switch-on methods.

    These experiments have shown that separating the 5V supply line of the SRAM and afferent buffers through a 1R resistor, which together with the tank capacitor acts as a low-pass filter, with a cut-off frequency of about 340 Hz, is sufficient to prevent any memory contents alteration at power-up.
    The corresponding modifications to the interface’s board, asillustrated below, can be easily performed within 5 minutes.

 
 
 
08 Dec 2013
    Corrected the joystick 'auto-fire' issue in GBL