# HG changeset patch # User Paul Boddie # Date 1550847935 -3600 # Node ID bb63d97d265e928978bbbc1b252dd9f5be2acb85 # Parent d4fc92a0628e570060e04dbfd5e4ee62182d8537 Added some notes about video expansions and ULA simplification. diff -r d4fc92a0628e -r bb63d97d265e Electron.txt --- a/Electron.txt Wed Apr 12 16:09:28 2017 +0200 +++ b/Electron.txt Fri Feb 22 16:05:35 2019 +0100 @@ -83,7 +83,10 @@ disabling the video signal, effectively achieving the same as blanking the palette, would be a very simple but useful enhancement that would speed up programs needing to render large amounts of non-real-time content to the -screen. +screen. This would also have been beneficial for display expansions connected +to the main expansion bus, along the lines of the Jafa MODE 7 adapter, where a +peripheral would maintain its own framebuffer by registering writes on the bus +to the display memory region. Improving Display Capabilities ------------------------------ @@ -110,6 +113,24 @@ low-memory screen mode usage - in order to retain as much content in memory as possible - would also be diminished. +Simplifying the ULA +------------------- + +An apparent motivation in the design of the Electron was to reduce the chip +count. However, this then requires that the ULA perform a range of different +roles. Some roles, such as handling cassette input and output, might have been +natural for the ULA given Acorn's previous designs, but others, such as +generating sound, arguably demand the integration of a lot of additional +functionality unless the capabilities are significantly reduced. Obviously, in +the Electron, the sound capabilities were reduced to a point where they were +considered a weakness of the machine. + +The design of the Commodore Plus/4 also sought to increase integration - +combining the sound and video chips in that case - but this was arguably more +feasible given the fabrication technology available within Commodore. +Meanwhile, Acorn might have been better off retaining a separate sound chip +and designing the ULA to interface with it instead. + About this Document -------------------