Hi! Larry Anderson wrote: > > There isn't one. This is a 6529 single port interface (data sheet on > > funet). When you read that address, all 8 data lines are read. When you > > write, all 8 data lines are written. > > That's like the PET then, the DDR on it does not do much in relation to > this interface (on the VIC and 64 the DDR is very important)... so I'll > just define an unused location in the BASIC example. In fact the 6529B works by the well known NMOS trick that probably most Commodore people know well (some maybe even if just waken up from sleep ;-) ). The NMOS outputs can't provide strong HI levels. The 6529B input port always gives back the current state of the port lines. If you want to use a line as input, first write '1' to the appropriate output bit. Since the NMOS high outputs are weak, the outputs can be pulled low by an external line. If something pulled the line low, the appropriate bit in the data register will be 0. L. - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tcm.hut.fi.
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