# HG changeset patch # User Paul Boddie # Date 1465299638 -7200 # Node ID da88a2fa37d8473595cdb01309264c6249a8be55 # Parent 89b5767d944def0c6e7514de886db19729d93a96 Updated Amstrad CPC-related notes concerning extra colour information. Added some links. diff -r 89b5767d944d -r da88a2fa37d8 ULA.txt --- a/ULA.txt Mon Oct 12 16:36:54 2015 +0200 +++ b/ULA.txt Tue Jun 07 13:40:38 2016 +0200 @@ -315,6 +315,8 @@ 2. Where a ROM numbered from 0 to 7 is to be selected, set bit 3 to zero whilst writing the desired ROM number n in bits 0 to 2. +See: http://stardot.org.uk/forums/viewtopic.php?p=136686#p136686 + Shadow/Expanded Memory ---------------------- @@ -374,6 +376,8 @@ trivial change). Another pitfall is the complication that might be introduced to software writing bitmaps of character height to the screen. +See: http://pastraiser.com/computers/acornelectron/acornelectron.html + Enhancement: The Missing MODE 4 ------------------------------- @@ -527,22 +531,22 @@ a single output line for each of the red, green and blue channels, and if those outputs are strictly digital and can only be set to a "high" and "low" value, then only the existing eight colours are possible. If a modern ULA were -able to output analogue values, it would still need to be assessed whether the -circuitry could successfully handle and propagate such values. Various sources -indicate that only "TTL levels" are supported by the RGB output circuit, and -since there are 74LS08 AND logic gates involved in the RGB component outputs -from the ULA, it is likely that the ULA is expected to provide only "high" or -"low" values. +able to output analogue values (or values at well-defined points between the +high and low values, such as the half-on value supported by the Amstrad CPC +series), it would still need to be assessed whether the circuitry could +successfully handle and propagate such values. Various sources indicate that +only "TTL levels" are supported by the RGB output circuit, and since there are +74LS08 AND logic gates involved in the RGB component outputs from the ULA, it +is likely that the ULA is expected to provide only "high" or "low" values. Short of adding extra outputs from the ULA (either additional red, green and -blue outputs or a combined intensity output, the former employed on the -Amstrad CPC series), another approach might involve some kind of modulation -where an output value might be encoded in multiple pulses at a higher -frequency than the pixel frequency. However, this would demand additional -circuitry outside the ULA, and component RGB monitors would probably not be -able to take advantage of this feature; only UHF and composite video devices -(the latter with the composite video colour support enabled on the Electron's -circuit board) would potentially benefit. +blue outputs or a combined intensity output), another approach might involve +some kind of modulation where an output value might be encoded in multiple +pulses at a higher frequency than the pixel frequency. However, this would +demand additional circuitry outside the ULA, and component RGB monitors would +probably not be able to take advantage of this feature; only UHF and composite +video devices (the latter with the composite video colour support enabled on +the Electron's circuit board) would potentially benefit. Flashing Colours ---------------- @@ -920,6 +924,7 @@ of the functionality exposed via the &FE*6 interface. See: http://en.wikipedia.org/wiki/Texas_Instruments_SN76489 +See: http://www.smspower.org/Development/SN76489 Enhancement: Waveform Upload ----------------------------