ZX Spectrum ULA: Difference between revisions

ZX Spectrum ULA (view source)

581 bytes added , 11 October 2011

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 From Z80 code, the ULA functions are accessible on any even-numbered I/O port (as the ULA performs ''very'' partial port decoding), but conventionally port 0xFE is used.
-''(list of the port high bytes & their interpretations should go here)''
+IN from port xxFE will read the keyboard state and tape input.  Each bit of the high byte selects a keyboard half-row; that row is read if the bit is ''low''.  If a key is pressed on any selected half-row, the corresponding bit of the data byte is ''low''; this accounts for bits d<sub>0</sub>-d<sub>4</sub>.  d<sub>6</sub> is the value at the EAR socket <sup>''(polarity?)''</sup>; d<sub>5</sub> and d<sub>7</sub> are not used.
-''(stuff about keyboard half-rows should go here)''
+OUT to port xxFE (the high byte is ignored) will set the border colour to {d<sub>2</sub>, d<sub>1</sub>, d<sub>0</sub>}, drive the MIC socket with d<sub>3</sub> and the loudspeaker with d<sub>4</sub>.<sup>''(again, polarity?)''</sup>  d<sub>5</sub>-d<sub>7</sub> are not used.
 == Contention ==