HP48/38 overhead projector interface


The HP38 has a direct connection for an external LCD (intended for an overhead projector). The HP48 requires a plug-in card. The HP48 bus doesn't seem to include any signal for vertical sync : on the HP38 this may be provided as the pin 'VCO' (but I haven't got one, so I can't check).

Can anyone tell me how the vertical sync signal is generated on an HP48 card ? Is it encoded somehow into the data stream (there are more bits in a line than are needed for the 131 pixels), or does it rely on software in the HP48 to drive hardware in the card ?

Is the 'VCO' signal on the HP38 interface a vertical sync, or is it something else ?


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