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50 lines
2.0 KiB
Plaintext
50 lines
2.0 KiB
Plaintext
The lower 8 bits of Timex SCLD ports are fully decoded
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Timings appear close to 48K spectrum despite the higher clock speed
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Keyboard reads (port FE) are different to other spectrum models, bits 5 & 7 are
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always reset
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Reading unattached ports gives 255. There are no floating ULA values.
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Joystick is returned for ports with bit 5 == 0
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Machine is silent during loading (eerie!)
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Colours are always bright in hires mode
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Border always matches hires colour in hires mode
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Short information about graphics modes of Timex.
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Modes are switched by port 255.
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They are:
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0 - standard Spectrum
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1 - the same in nature as 0, but using second display file
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2 - extended colours (data taken from first screen,
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attributes 1x8 taken from second display.
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3 - similar to 2, but data is taken from second screen
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4 - hires mode, data in odd columns is taken from first screen
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in standard way, data in even columns is made from attributes data (8x8)
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5 - similar to 4, but data taken from second display
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6 - true hires mode, odd columns from first screen, even columns from
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second screen. I mean columns numbered from 1.
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7 - data taken only from second screen, columns are doubled
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Hires mode (4,5,6,7) are monochrome. Ink, paper (border the same as paper)
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depends on bits 3,4,5 of data sent to port 255, eg.
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OUT 255,6 WHITE & BLACK
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OUT 255,14 YELLOW & BLUE
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OUT 255,22 CYAN & RED
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and so on.
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The problem of accurate Timex SCLD (ULA) emulation
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--------------------------------------------------
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The Timex machines produce displays that are almost, but not quite, the same as
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those produced by a 48K Spectrum. Aquaplane has a perfectly aligned border
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effect, Academy's menu border effect is out one border line on one side only.
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Running a contention test (based on contention from fusetest) shows that the
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contention pattern starts at 14320 with 6, then 5, 4, 3, 2, 1, 0, 0 in the same
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way as the Sinclair ULA.
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It seems that the display of the top left pixel is slightly out of sync with
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this and the first pixel is displayed at 14321 based on the output of other
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contention testing programs.
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