1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/Electron.txt Mon Jan 09 00:34:03 2012 +0100
1.3 @@ -0,0 +1,54 @@
1.4 +Potential Design Improvements for the Acorn Electron
1.5 +====================================================
1.6 +
1.7 +The Acorn Electron was designed to be a variant of the BBC Microcomputer that
1.8 +was intended to be simpler, easier and cheaper to produce whilst retaining a
1.9 +degree of compatibility and offering many of the same features, principally
1.10 +the wide range of graphics modes, BBC BASIC, and extensible hardware and
1.11 +software capabilities. Upon its introduction in late 1981, the BBC Micro
1.12 +competed favourably against its immediate contemporaries, such as the ZX81 and
1.13 +VIC-20, as well as machine introduced slightly later, such as the ZX Spectrum
1.14 +and Commodore 64. By producing a less expensive machine that retained certain
1.15 +key features, the motivation was to bring BBC Micro technology to bear on the
1.16 +lower end of the home computer market, albeit approximately two years after
1.17 +its initial introduction.
1.18 +
1.19 +Unfortunately, various features were omitted from the Acorn Electron that made
1.20 +it less competitive than it could have been against a steadily improving range
1.21 +of competitors: multi-channel sound support, MODE 7 teletext, support for
1.22 +relatively smooth horizontal hardware scrolling (and other display control
1.23 +features), and the double-speed bus with interleaved CPU and video access.
1.24 +More RAM would also have been beneficial, although costly at the prices of the
1.25 +day. Such deficiencies outweighed the significant benefits of substantial
1.26 +software compatibility, and some of them effectively curtailed that
1.27 +compatibility by making even reasonably well-written software titles
1.28 +effectively unusable, particularly games relying on the BBC Micro's hardware
1.29 +scrolling capabilities, including "official" Acornsoft titles.
1.30 +
1.31 +In hindsight, numerous features could be suggested that would make the
1.32 +Electron more competitive, but many of these features would incur a
1.33 +substantial cost. For example, giving the Electron 64K of RAM would have
1.34 +increased the price substantially. Introducing the double-speed bus and faster
1.35 +memory may also have increased the price in a prohibitive fashion. Thus, it
1.36 +becomes worthwhile to consider minimal alterations to the machine's
1.37 +specification that offer the greatest benefits for the least additional cost.
1.38 +
1.39 +Improving System Performance
1.40 +----------------------------
1.41 +
1.42 +Although RAM is accessed by the CPU at 1MHz, ROM is accessed at 2MHz. Thus,
1.43 +deploying software that runs from ROM can potentially provide significant
1.44 +performance benefits. Since the unexpanded Electron provides no convenient
1.45 +means of installing ROM-based software - the Plus 1 and other expansion units
1.46 +offered ROM cartridge slots, and various expansions provided ROM sockets - the
1.47 +improved Electron would ideally need to have a ROM cartridge slot. A
1.48 +side-benefit of adding this feature would arguably be an increased demand for
1.49 +cartridge-based software, potentially at a slightly higher price and also
1.50 +offering additional hardware features if necessary, thus making any cost
1.51 +incurred in the manufacture of the base unit more bearable.
1.52 +
1.53 +The Slogger/Elektuur turbo board modified the system to permit the CPU to
1.54 +access the bottom 8K of RAM without interruption by the ULA. This feature,
1.55 +already known at Acorn during the Electron's design period, permitted
1.56 +substantial improvements to performance and could also be incorporated into an
1.57 +improved Electron.
2.1 --- a/ULA.txt Tue Dec 20 00:56:33 2011 +0100
2.2 +++ b/ULA.txt Mon Jan 09 00:34:03 2012 +0100
2.3 @@ -11,6 +11,12 @@
2.4 See: Acorn Electron Advanced User Guide
2.5 See: http://mdfs.net/Docs/Comp/Electron/Techinfo.htm
2.6
2.7 +Access to RAM involves accessing four 64Kb dynamic RAM devices (IC4 to IC7,
2.8 +each providing two bits of each byte) using two cycles within the 500ns period
2.9 +of the 2MHz clock to complete each access operation.
2.10 +
2.11 +See: Acorn Electron Service Manual
2.12 +
2.13 Hardware Scrolling
2.14 ------------------
2.15