1.1 --- a/ULA.txt Mon Oct 12 16:36:54 2015 +0200
1.2 +++ b/ULA.txt Tue Jun 07 13:40:38 2016 +0200
1.3 @@ -315,6 +315,8 @@
1.4 2. Where a ROM numbered from 0 to 7 is to be selected, set bit 3 to zero
1.5 whilst writing the desired ROM number n in bits 0 to 2.
1.6
1.7 +See: http://stardot.org.uk/forums/viewtopic.php?p=136686#p136686
1.8 +
1.9 Shadow/Expanded Memory
1.10 ----------------------
1.11
1.12 @@ -374,6 +376,8 @@
1.13 trivial change). Another pitfall is the complication that might be introduced
1.14 to software writing bitmaps of character height to the screen.
1.15
1.16 +See: http://pastraiser.com/computers/acornelectron/acornelectron.html
1.17 +
1.18 Enhancement: The Missing MODE 4
1.19 -------------------------------
1.20
1.21 @@ -527,22 +531,22 @@
1.22 a single output line for each of the red, green and blue channels, and if
1.23 those outputs are strictly digital and can only be set to a "high" and "low"
1.24 value, then only the existing eight colours are possible. If a modern ULA were
1.25 -able to output analogue values, it would still need to be assessed whether the
1.26 -circuitry could successfully handle and propagate such values. Various sources
1.27 -indicate that only "TTL levels" are supported by the RGB output circuit, and
1.28 -since there are 74LS08 AND logic gates involved in the RGB component outputs
1.29 -from the ULA, it is likely that the ULA is expected to provide only "high" or
1.30 -"low" values.
1.31 +able to output analogue values (or values at well-defined points between the
1.32 +high and low values, such as the half-on value supported by the Amstrad CPC
1.33 +series), it would still need to be assessed whether the circuitry could
1.34 +successfully handle and propagate such values. Various sources indicate that
1.35 +only "TTL levels" are supported by the RGB output circuit, and since there are
1.36 +74LS08 AND logic gates involved in the RGB component outputs from the ULA, it
1.37 +is likely that the ULA is expected to provide only "high" or "low" values.
1.38
1.39 Short of adding extra outputs from the ULA (either additional red, green and
1.40 -blue outputs or a combined intensity output, the former employed on the
1.41 -Amstrad CPC series), another approach might involve some kind of modulation
1.42 -where an output value might be encoded in multiple pulses at a higher
1.43 -frequency than the pixel frequency. However, this would demand additional
1.44 -circuitry outside the ULA, and component RGB monitors would probably not be
1.45 -able to take advantage of this feature; only UHF and composite video devices
1.46 -(the latter with the composite video colour support enabled on the Electron's
1.47 -circuit board) would potentially benefit.
1.48 +blue outputs or a combined intensity output), another approach might involve
1.49 +some kind of modulation where an output value might be encoded in multiple
1.50 +pulses at a higher frequency than the pixel frequency. However, this would
1.51 +demand additional circuitry outside the ULA, and component RGB monitors would
1.52 +probably not be able to take advantage of this feature; only UHF and composite
1.53 +video devices (the latter with the composite video colour support enabled on
1.54 +the Electron's circuit board) would potentially benefit.
1.55
1.56 Flashing Colours
1.57 ----------------
1.58 @@ -920,6 +924,7 @@
1.59 of the functionality exposed via the &FE*6 interface.
1.60
1.61 See: http://en.wikipedia.org/wiki/Texas_Instruments_SN76489
1.62 +See: http://www.smspower.org/Development/SN76489
1.63
1.64 Enhancement: Waveform Upload
1.65 ----------------------------