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Chapter 4

Display file:

Attributes file:

The area number is specified by bits An, the row number within an area by bits Rn, the

pixel line number within a row by bits Ln and the column number by bits Cn. It can be

seen that the lower 8 bits are identical between the display file and the attributes file,

and this approach was used since it simplified the picture generation logic inside the

ULA. Note that the A0 and A1 bits never both hold a value of 1, and thus the display

file and the attributes file can never overlap.

The new attribute modes provided by the SPECTRA interface use an addressing

scheme for the display file that is identical to that used by the standard Spectrum

screen. However, the addressing schemes used for the various display mode attribute

files are different. A relationship between them and the display file can be seen by

examining address lines A8 to A12, which shift by one bit position to the left each time

the vertical colour resolution is doubled. It becomes clear that although the standard

attributes file (row mode) visually appears to be a logical progression, it can actually be

thought of as an extreme case of the ‘odd’ sequence seen in the display file. The

addressing schemes for the new attribute modes are shown below.

Display file:

Row mode:

Quad line mode:

Dual line mode:

Single line mode – basic / extra colours using single byte colour:

Single line mode – basic / extra colours using double byte colour:

Single line area:

Dual line area:

The bit denoted by D applies to double byte colour and its action depends upon the

full / half cell bit of the display mode register. In full cell mode and in half cell mode

Sinclair ZX Spectrum User Manual

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