Acorn Electron
The Acorn Electron was an affordable version of the BBC Micro study and home computer manufactured by Acorn . It was equipped with 32 kB of RAM and its ROM contained BBC BASIC and the operating system .
The Electron used audio cassettes to load and save programs. A converter cable was included for this purpose, which enabled connection to a standard cassette recorder with suitable sockets . It could output simple graphics on a television, RGB monitor, or green monitor.
At its heyday, the Electron was the third most popular microcomputer in the UK , and overall more games were sold than the BBC Micro. There are at least 500 known games for the Electron.
The hardware of the BBC Micro was essentially integrated in a single chip that was developed by Acorn and implemented on the basis of an adapted ULA . Because of the design, capabilities were limited, such as limiting audio output to one channel while the BBC Micro had three channels (and one for noise). In addition, it could not offer a teletext mode .
The ULA controlled the memory access and was able to address 32K × 8 bits of RAM, with 4 pieces of 64K × 1-bit RAM chips of the type 4164 being used. Because each chip had to be accessed twice (instead of just one), and because the video hardware also had to access the memory, reading and writing in RAM was slower than with the BBC Micro. While pure ROM applications ran just as fast, applications with RAM access suffered significant speed losses.
history
The Electron was designed in 1983 as the lower cost brother of the BBC Micro. The aim was to secure the low-price segment for the Christmas business. Even though Acorn had managed to offer practically the same functionality as the BBC Micro in a single chip, manufacturing problems meant that only a few units were available for the holiday season.
Sales never fully recovered from this setback, although ultimately more games were sold for the Electron than for the BBC Micro. After Olivetti's stake in Acorn in 1985, the Electron was practically sidelined.
In retrospect, it becomes clear that the Electron's memory was too small. Only about 20 kB were available to a program after the graphics memory was removed. The Electron couldn't compete with the processing speed of a Sinclair ZX Spectrum or Commodore 64 either . Nevertheless, many functions that were later linked to the BBC Master and Archimedes were first offered by expansion modules for the Electron. Examples of this are ROM cartridges and the Advanced Disc Filing System , which was a further development of the Disc Filing System for the BBC Micro.
Even if the Electron is not considered to be very successful compared to its competitors such as Spectrum, Commodore 64, Amstrad CPC or the BBC Micro, the sales figures were so good that new software was available until the early 1990s. That means the electron had a lifespan no less than that of more popular microcomputers.
Popular upgrades
Acorn Plus 1
With the Acorn Plus 1 version, two ROM slots, an analog interface and a parallel port became available. The analog interface was mostly used to connect joysticks , the parallel port usually for printers .
Access to the ROM memory was clocked at 2 MHz regardless of the graphics mode. This allowed programs available on ROM to run theoretically twice as fast as programs distributed on tape or floppy disk . However, all games published on ROM came as 'serial ROMs' from which the computer read the programs as if they were off tape. Although this had the advantage that programs did not have to be adapted to their new memory address, it also did not increase the speed.
Acorn Plus 3
The Acorn Plus 3 was a hardware module that was connected independently of the Plus 1 and offered a connection option for a 3½ ”floppy disk drive. The drive was made possible via a WD1770 controller from Western Digital and a ROM for the ADFS . Because the controller could also deal with simple storage density and used the same diskette format derived from the IBM360 as the Intel 8271 in the BBC Micro, it was possible to use the DFS file system with an exchange ROM .
First byte joystick interface
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The Electron, like the Sinclair Spectrum, was initially unsuitable as a game computer because it lacked a joystick port. Therefore, First Byte Computers offered a very popular interface, including software, which allowed a joystick to be used with a majority of the available programs.
PRES Advanced Plus 3
The Advanced Plus 3 was very similar to the Acorn Plus 3 but was offered as a ROM cartridge for the Plus 1 with a connected connector for a floppy disk drive. It was possible to connect a 5¼ ”floppy disk drive, as used by users of the BBC Micro, or one of the more common 3½” drives.
Slogger / Elektuur Turbo Board
The Slogger and Elektuur Turbo Boards emerged from a hack invented by Acorn. By placing the lower 8 kB of RAM outside of the ULA's access, the CPU's access speed to this area was always 2 MHz. However, the graphics memory could not be placed in this 8 kB. Most of the time, the operating system ROMs put the graphics memory in the upper 24 kB, so that only 2% of the software was incompatible.
The Slogger Turbo Board was a professionally made upgrade module. The adjustments for the Elektuur board were described in the Dutch electronics magazine Elektuur (the Dutch parent edition of Elektor ) and could be copied by readers.
For computers derived from the 6502 , the acceleration of access to the lower memory area was particularly advantageous, since the processor offers a faster type of addressing for the first 256 bytes . Therefore, variables that were required for time-critical operations were usually placed in this area.
Slogger Master RAM Board
The Slogger Master RAM Board was a further development of the Turbo Board and, as an additional function, offered the option of operating the Electron with 32 kB of shadow RAM in addition to the 32 kB already available.
By skillfully manipulating the command counter , it was possible that the normal system ROMs and software that the operating system calls use could be used without extensive changes. This made more memory available for BASIC , View, Viewsheet and other business applications. The modification made additional memory available so that some games and applications could run for the BBC Micro, even if the Electron lacked a native mode 7 for display.
Applications could not access the graphics memory without changing the program code. As a result, the expansion was incompatible with most games, even if there was no need to program a game to work in shadow mode.
During the downturn, each Electron Master RAM board was included to increase sales.
Jafa Systems Mode 7 Display Unit
One of the features of the BBC Micro that the Electron lacked was Teletext Mode 7 . The lack of this mode is surprising in view of the low memory usage of less than 1 kB in this mode and the large number of BBC micro programs that use this mode. Jafa Systems offered some solutions to retrofit or at least emulate the missing mode.
The simplest solution was a pure software system, which was delivered as a ROM module and which approximated Mode 7 in graphics mode - albeit in a low resolution. Even if this approach was inexpensive and effective in enabling some programs to output text in Mode 7 via official entry points, this solution was also very slow. One of the reasons for this was that the approximation had to be calculated by the Electron's CPU, which is not necessary in a native mode such as the BBC Micro. The memory required was also significantly larger at 20 kB.
There were also two solutions with additional hardware. The first was based on the SAA5050 graphics processor used by BBC Micro in Mode 7. The solution also consisted of a piece of software that ensured that the processor was supplied with the necessary graphics data. The ULA continued to access the graphics memory while the SAA5050 read out this data and provided a mode 7 interpretation of the data. The hardware part switched between the graphics output of the Electron and the module if necessary.
The disadvantage of this system was that the SAA5050 had to be repeatedly supplied with the same 40 bytes of data per image line and character line, while the ULA read a different set of 40 bytes per image line in order to enable display in native mode. The software part circumvented this problem by duplicating the data for mode 7 display in memory. As a result, there was hardly any loss of performance in the display in mode 7, which was qualitatively identical to that of the BBC Micro. The solution, however, required 10 kB of memory and was only compatible with programs that used the ROM routines to output text and graphics.
A second version of the hardware solution eliminated these problems. A Motorola 6845 (CRTC) was added to this. The solution was based entirely on hardware, had no negative impact on execution speed and only used 1 kB of memory for graphics output. There was still a software ROM, but it only expanded the hardware ROM so that it could switch to mode 7.
Merlin M2105
An unusual variant of the Electron was offered by British Telecom Business Systems as the BT Merlin M2105 Communications Terminal . It was an electron from which the nameplate was removed and an extensive expansion module was added. This extension consisted of an additional 32 kB of RAM and 48 kB of ROM, a Centronics connection for a printer and a modem . The firmware of the ROM enabled communication via the modem. The terminals have been used by the Interflora network of florists in the UK for over ten years .
Technical specifications
hardware
- CPU : MOS Technology 6502
- Clock frequency: The processor has a clock frequency of 2 MHz when accessing the ROM and 1 MHz or 0.5897 MHz when accessing the RAM (depending on the graphics mode). The frequent (and incorrect) mention of a clock frequency of 1.79 MHz is based on speed comparisons with the BBC Micro, which was clocked consistently with 2 MHz.
- Coprocessor: Ferranti Semiconductor Custom ULA
- RAM : 32 kB
- ROM : 32 kB
- Text modes: 20 × 32, 40 × 25, 40 × 32, 80 × 25, 80 × 32. In graphic modes, the entire text output was generated by software.
- Graphic modes: 160 × 256 (4 or 16 colors), 320 × 256 (2 or 4 colors), 640 × 256 (2 colors), 320 × 200 (2 colors, with two empty lines output after every 8 pixel lines), 640 × 200 (2 colors)
- Colors: 8 colors (combination of the RGB primary colors) + 8 flashing versions of the colors
- Tone: 1 tone channel, 7 octaves; built-in speaker. Software emulation of the noise channel is supported.
- Dimensions: 16 × 34 × 6.5 cm
- Ports for input and output: Expansion port, connection for a tape recorder (1200 baud , variation of the Kansas City standard for encoding data), antenna connection for the television ( HF modulator ), output of composite video and for RGB monitors
- Power supply: external power supply unit, 18 V AC
Quirks
Like the BBC Micro, the Electron was limited because of its low storage capacity. Of the 32 kB RAM, 3.5 kB was reserved for the operating system at startup and at least 10 kB was used as a buffer for the graphics memory.
The timing of interrupts made it possible to switch off either the upper 100 or the lower 156 lines of the display. Many games took advantage of this and saved non-graphic data in the deactivated area in order to be able to use the additional space differently. Other games loaded non-graphical data into screen memory so that it was displayed as pixels with seemingly random colors.
The hardware allowed page flipping to create fluid animations. However, the limited memory forced most applications to write their output directly to screen memory, causing flickering or visible redrawing. One exception is the Joe Blade series from Players.
Well-known games
In contrast to the Commodore 64 or the Sinclair ZX Spectrum, the Electron did not enjoy the broad support of the major game manufacturers. However, many games have been released for the Electron, particularly by game makers for the BBC Micro such as Acornsoft , Superior Software and Micro Power . Popular games that are particularly associated with the Electron are:
- Starship Command (Acornsoft, 1983)
- Chuckie Egg (A'n'F, 1984)
- Elite (Acornsoft, 1984)
- the Repton series (Superior Software, 1985–1989)
- Thrust (Superior Software, 1986)
- Exile (Superior Software, 1988)
Many popular games have also been officially converted from arcade machines . These included Crystal Castles , Tempest , Commando , Paperboy and Yie Ar Kung-Fu . Games converted from other home computers included Impossible Mission , Jet Set Willy , The Way of the Exploding Fist , Tetris , The Last Ninja , Barbarian, and SimCity .
Although Acorn effectively discontinued the Electron in 1985, games for the Electron continued to be developed and published until 1991. In addition to the approximately 1400 games that were published for the Acorn Electron (99% of them on cassette), there were also thousands of programs that were published as public domain on floppy disk. These disks were distributed by BBC PD , the Electron User Group and HeadFirst PD , among others .
emulation
There are three emulators for the computer: ElectrEm for Windows / Linux / Mac OS X , Elkulator for Windows / DOS and multisystem emulator MESS software for Electron is mainly in the UEF - file format archived.
Individual evidence
- ^ Andy's guide to using BBC software on a 64K modified Acorn Electron. Retrieved June 11, 2010 .
- ↑ Jafa Systems Mode 7 Display Unit. User Guide. (Word file; 76 kB) (No longer available online.) Archived from the original on March 30, 2007 ; accessed on June 19, 2010 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Data sheet of the SAA5050 for Mode 7 of the BBC Micro. (PDF; 667 kB) (No longer available online.) Archived from the original on March 3, 2016 ; accessed on June 18, 2010 (English).
- ↑ Data sheet of the SY6845 from Synertek. (PDF file; 2.6 MB) Retrieved June 18, 2010 (English).
- ↑ Acorn Merlin M2105 Communications Terminal ( Memento February 4, 2012 in the Internet Archive ) Acorn Electron World
Web links
- Acorn Electron World
- bygonebytes Comprehensive page on the Acorn Electron
- ElectrEm emulator for the Acorn Electron
- Elkulator emulator for the Acorn Electron