Editing Acorn Electron (section)

====Acorn Plus 3====
[[File:Acorn ALA13 Electron Plus 3 (front).jpg|thumb|Acorn Plus 3, showing the connector and disc drive]]
Launched in late 1984 for a price of £229,<ref name="popcompweekly19841122">{{ cite news | url=https://archive.org/details/popular-computing-weekly-1984-11-22/page/n4/mode/1up | title=New Acorn products at Compec | work=Popular Computing Weekly | date=22 November 1984 | access-date=28 December 2020 | page=5 }}</ref> the Acorn Plus 3 was a hardware module that connected independently of the Plus 1 and provided a "self contained disc interface and 3.5 inch single sided disc drive" offering over 300&nbsp;KB of storage per disc using the newly introduced [[Advanced Disc Filing System]] (ADFS).<ref name="plus3">{{ cite book | url=http://www.4corn.co.uk/archive/docs/AMPAPP/150/AMP056%20-%20Electron%20Plus%203-opt.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.4corn.co.uk/archive/docs/AMPAPP/150/AMP056%20-%20Electron%20Plus%203-opt.pdf |archive-date=2022-10-09 |url-status=live | title=Electron Plus 3: New dimensions in capability | publisher=Acorn Computers Limited | page=2 }}</ref> The Plus 3 was also reportedly produced with a double-sided drive fitted.<ref name="electronuser198503_plus3">{{ cite magazine | url=https://archive.org/details/ElectronUserVolume2/Electron-User-02-06/page/n34/mode/1up | title=...and then there was Plus 3 | magazine=Electron User | date=March 1985 | volume=2 | issue=6 | access-date=6 March 2021 | last1=Peters | first1=Nigel | page=35 | quote=Some versions of the Plus 3 allow both sides of the disc to be used, allowing 640k of information to be stored. }}</ref>

An expansion connector for a second 3.5- or 5.25-inch drive was also provided by the unit, with such drives needing to provide a [[Shugart bus|Shugart]]-compatible connector and their own power supply.<ref name="plus3ug">{{ cite book | url=http://chrisacorns.computinghistory.org.uk/docs/Acorn/Manuals/Acorn_Plus3UG.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://chrisacorns.computinghistory.org.uk/docs/Acorn/Manuals/Acorn_Plus3UG.pdf |archive-date=2022-10-09 |url-status=live | title=The Electron Plus 3 User Guide | publisher=Acorn Computers Limited | date=October 1984 | issue=1 | access-date=6 March 2021 }}</ref>{{rp|page=4}} The original Electron edge connector was repeated on the back of the Plus 3, allowing the Plus 1 or other compatible expansion to be connected in conjunction with the Plus 3.<ref name="plus3ug" />{{rp|page=5}}

The double-density drive of the Plus 3 was driven using a [[WD1770]] drive controller by the ADFS. (The Plus 3 had been rumoured to offer Acorn's DFS and to feature an 8272 double-density [[disk controller]] before its launch.<ref name="electronuser198411">{{ cite magazine | url=https://archive.org/details/ElectronUserVolume2/Electron-User-02-02/page/n4/mode/1up | title=Electron disc drive - and it's official | magazine=Electron User | date=November 1984 | access-date=13 January 2021 | page=5 }}</ref>) Because the WD1770 is capable of single-density mode and uses the same IBM360-derived floppy disc format as the Intel 8271 found in the BBC Micro, it was also possible to use the [[Disc Filing System]] with an alternate ROM, such as the ACP 1770 DFS.<ref name="electronuser198602_acp1770dfs">{{ cite magazine | url=https://archive.org/details/ElectronUserVolume3/Electron-User-03-05/page/n53/mode/1up | title=ROMs | magazine=Electron User | date=February 1986 | volume=3 | issue=5 | access-date=6 March 2021 | last1=Waddilove | first1=Roland | page=54 }}</ref>

The Plus 3 reset PAGE to &1D00, reducing the amount of free RAM available to the user.<ref name="plus3ug" />{{rp|page=52}} The ADFS system could be temporarily disabled (and PAGE reset to &E00) via the {{kbd|*NOADFS}} command.<ref name="plus3ug" />{{rp|page=15}} Later products such as the PRES E00 ADFS remedied the memory demands of the ADFS, along with other issues suffered by the software as delivered with the Plus 3.<ref name="electronuser198808" /> If using the Plus 3 in screen modes 0–3, the pseudo-variable {{mono|TIME}} would be thrown off, as the interrupts were disabled during disk access in these modes. The screen would also blank during disc accesses.<ref name="plus3ug" />{{rp|pages=14–15}}

Disks had to be manually [[Mount (computing)|mounted]] and dismounted using the {{kbd|*MOUNT}} / {{kbd|*DISMOUNT}} commands, or using the {{keypress|Ctrl}}+{{keypress|A}}+{{keypress|Break}} key combination. Disks could also be booted from via the standard {{keypress|Shift}}+{{keypress|Break}} key-combination, if the !BOOT file was present on the disk. This behaviour was the same as on the BBC Micro.<ref name="plus3ug" />{{rp|page=18}}

The Plus 3 included an uprated square black power supply unit with mains cord, manufactured by STC, designed and manufactured in England to {{nowrap|[[British Standards|BS]] 415}} and {{nowrap|BS 5850}}, that was designed to power the Plus 3, in addition to the Electron and the Plus 1 interface as well.<ref name="acorn_mains_adaptor">{{cite web | url=http://www.stardot.org.uk/forums/download/file.php?id=4417 | title=Plus 3 Disc Unit Mains Adaptor (36 watts) | date=4 October 1984 | issue=2 | access-date=14 March 2021 }}</ref> This replaced the original cream-coloured "wall wart" style power supply, designed to {{nowrap|BS 415}} and manufactured in Hong Kong.

* '''Original''' Part no: 0201,113;<ref name="acorn_do_0201">{{ cite tech report | url=http://www.4corn.co.uk/archive/do/registers/x201/0201.txt | title=0201 DETAIL DRAWINGS | publisher=Acorn Computers Limited | access-date=14 March 2021 }}</ref> input 220/240 V AC/50&nbsp;Hz; output 19 V AC/0.737 A/14 W:  '''Usage''': Electron, Electron+Plus1
* '''Uprated''' Part no: 0865,010; input 240&nbsp;V AC/50&nbsp;Hz 50&nbsp;W; output 21&nbsp;V AC/1.75&nbsp;A/36.75&nbsp;W: '''Usage''': Electron+Plus3, Electron+Plus3+Plus1

Repair note: If the internal power-supply connector, used to power the existing internal 3.5-inch drive is damaged, and requires replacement, then the original AMP 800-930 4-pin connector, which was already in short supply during the original production run, may be replaced with a Molex 5264 50-37-5043 "Mini-SPOX" connector as an alternative.<ref name="acorn_memo">{{cite tech report | url=http://www.stardot.org.uk/forums/download/file.php?id=4417 | title=Acorn Electron Disc Drive Connector{{snd}} Internal Memo | publisher=Acorn Computers Limited | last1=Ashby | first1=Simon | date=7 September 1984 | access-date=14 March 2021 }}</ref>