Rewrite with citations from the newly hosted Acorn Archimedes 500 / R200 Service Manual and Chris Whytehead. Corrected: SCSI is a podule that occupies a slot, not on the motherboard, so all four slots are NOT free; the SCSI controller is a WD33C93A not an NCR 53C90; the FPA11 is not an A540 part. Added BT1 NiCd 1.2 V 280 mAh with the 2.8 V on IC22 pin 8 check, the MEMC part-number warning and the FPA10 price and early-card modification. Removed the unsourced oscillator frequencies, motherboar...
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| caption = Acorn Archimedes A540
| caption = Acorn Archimedes A540
| manufacturer = Acorn Computers Ltd
| manufacturer = Acorn Computers Ltd
| type = Personal Computer
| type = Personal computer (three-box desktop)
| release date = September 1990
| release date = June 1990
| discontinued = 1992
| discontinued = 1992
| price = £2,995 (1990)
| price = £2,495 ex VAT, no monitor
| cpu = ARM3 @ 26 MHz
| cpu = ARM3 on a replaceable CPU card, 25/26 MHz as shipped; 33 MHz cards exist
| memory = 4 MB RAM (expandable to 16 MB)
| memory = 4 MB RAM, expandable to 16 MB with up to three 4 MB RAM cards
The '''Acorn Archimedes A540''' was launched in June 1990 as the flagship of the Archimedes range. It was the first Acorn machine with an ARM3 as standard, the only one that could be taken to 16 MB of memory, and — with an ARM3 and an FPA10 fitted — more powerful than the later [[Acorn Archimedes A5000|A5000]].<ref name="chris540">Whytehead, Chris. [https://chrisacorns.computinghistory.org.uk/Computers/A540.html "Acorn Archimedes A540"], Chris's Acorns / The Centre for Computing History.</ref>
The '''Acorn Archimedes A540''' was introduced in September 1990 as the flagship model of the second-generation Archimedes range. First Archimedes to feature the ARM3 processor as standard, the A540 delivered unprecedented performance for the platform while introducing SCSI storage and enhanced memory capabilities that positioned it as a serious Unix workstation.
It costs £2,495 plus VAT without a monitor, and shares its hardware with Acorn's R260 RISC iX workstation: the A540 is an R260 without RISC iX installed, which could be bought separately and installed later.<ref name="chris540" /> Acorn documented the two together in the [[Acorn Archimedes 500 Series and R200 Series Service Manual]].<ref name="sm500">Acorn Computers Limited, ''Acorn Archimedes 500 series / Acorn R200 series Service Manual'', Issue 2, June 1991. Part 5 component-level fault diagnosis and Part 6 parts lists. Hosted on this wiki: [[Acorn Archimedes 500 Series and R200 Series Service Manual]].</ref>
== Overview ==
== Memory system ==
The A540 represented Acorn's response to criticism that the original Archimedes lacked the performance for professional workstation applications. The ARM3 processor, running at 26 MHz with 4 KB of cache memory, provided approximately four times the processing power of the ARM2-based models. Combined with a 100 MB SCSI hard drive and support for up to 16 MB of RAM, the A540 competed directly with entry-level Sun and HP workstations at a fraction of the cost.
This is what makes the A540 unusual. A single MEMC1a addresses a maximum of 4 MB, so Acorn put a MEMC1a on the motherboard and gave the machine three further sockets, SK5, SK6 and SK7, for '''RAM cards that each carry their own MEMC1a and their own 4 MB'''. Configurations are therefore 4, 8, 12 or 16 MB.<ref name="chris540" /><ref name="sm500" />
Acorn positioned the A540 primarily at the Unix workstation market, bundling RISC iX with many systems. The machine also attracted high-end educational users, CAD operators, and desktop publishing professionals who required maximum performance from the RISC OS platform. At £2,995, the A540 cost significantly more than the A440 it replaced, but delivered specifications that justified the premium for demanding applications.
The motherboard's DRAM is 1M × 1 80 ns in 20-pin ZIP packages; the 4 MB cards use 1M × 4 80 ns SOJ devices with a MEMC1a at IC10. Acorn's parts list carries an explicit warning: '''MEMCs must be Acorn part number 2201,393''' to guarantee correct timing.<ref name="sm500" /> The memory clock runs at '''12 MHz''', against 8 MHz on the A300, A400 and A400/1 machines.<ref name="chris540" /><ref name="sm500" /> Acorn and Simtec both made RAM cards.<ref name="chris540" />
== Architecture ==
The memory cards are the machine's known weak point. Chris Whytehead reports that an A540 left unused for a while becomes temperamental and that the RAM cards in particular are liable to work loose; reseating them is the first thing to try on an unstable machine.<ref name="chris540" />
The A540 introduced significant architectural improvements over first-generation machines. The ARM3 processor maintained instruction set compatibility with ARM2 while adding cache memory and higher clock speeds. The MEMC1a memory controller supported larger memory configurations through bank switching, while the enhanced VIDC20 video controller provided improved color depth and resolution support.
== Processor ==
=== ARM3 Processor ===
The ARM3 sits on a replaceable CPU card. Machines shipped with 25 or 26 MHz parts; 33 MHz cards exist and are found on upgraded machines. Chris Whytehead's two documented A540s carry a VL86C020 at 26 MHz (the original card, with no FPA socket) and a VY86C020-35 at 33 MHz with an FPA10 fitted.<ref name="chris540" />
The 4 KB cache proved crucial for performance, reducing memory bandwidth requirements by approximately 75% for typical code. Cache operation was fully transparent to software, with hardware maintaining coherency for DMA operations. The write-through design simplified implementation while providing substantial performance benefits.
=== FPA10 floating point accelerator ===
=== Memory System ===
Acorn released the FPA10 in July 1993 for the A540, the A5000 and the R260, at '''£99 ex VAT'''. It fits a socket designed for it on the A540's processor card. Acorn's figures: 250 mW dissipation, peak throughput up to 5 MFLOPS at 26 MHz and an average above 3 MFLOPS, with floating point performance under the RISC OS floating point emulator increasing by as much as a factor of 50.<ref name="prfpa">Acorn Computers Limited press release, "Acorn Releases Floating Point Accelerator", 5 July 1993. [https://chrisacorns.computinghistory.org.uk/docs/Acorn/PR/FPA_release.txt Text] via Chris's Acorns.</ref>
The A540 supported dramatically expanded memory configurations:
Acorn's own release note adds a repair-relevant point: '''owners of early A540s and R260s may need a free-of-charge modification to their processor cards''' before an FPA10 will work, and RISC iX users need an additional software driver.<ref name="prfpa" />
The standard MEMC1a controller addressed 4 MB directly. Larger configurations required the MEMC podule, which implemented bank switching to access additional memory. While RISC OS could only directly use 4 MB for applications, the additional memory served as RAM disc or cache for Unix operations.
== SCSI ==
== Hardware Specifications ==
The A540's SCSI is '''not''' on the motherboard. Unlike the rest of the range it shipped with a SCSI podule as standard, together with a 100 MB SCSI hard disc — so one of the four podule slots is occupied from new.<ref name="chris540" /> Documented machines carry the Acorn AKA31 (part 0173,010) or the AKA32 Mk3 (part 0173,080).<ref name="chris540" />
The A540 motherboard represented a significant revision from earlier models, optimized for the ARM3 processor and enhanced peripherals.
Acorn's service manual documents the SCSI expansion card down to component level. It is built around a '''Western Digital WD33C93A''' SCSI bus interface controller and an NEC 71071 DMA controller, with two 32K × 8 static RAMs, a driver EPROM and five PALs.<ref name="sm500" />
=== Motherboard Design ===
== Video ==
Key improvements included:
The A540 uses the VIDC1a, as the rest of the Archimedes range does.<ref name="chris540" /> It and the R260 carry '''three BNC connectors''' on the rear panel that appear on no other Acorn machine.<ref name="chris540" />
* '''Six-layer PCB:''' Improved signal integrity and EMI reduction
* '''Surface-mount technology:''' Reduced size and improved reliability
* '''Enhanced power distribution:''' Separate planes for digital and analog supplies
* '''Improved grounding:''' Star ground configuration reduced noise
* '''Modular connectors:''' Simplified assembly and service
The ARM3 processor mounted in a 160-pin QFP socket, allowing field replacement if necessary. The cache RAM utilized fast 15ns static RAM chips, essential for single-cycle operation at 26 MHz.
== Expansion and construction ==
=== SCSI Subsystem ===
The backplane is Acorn part 0186,001, four slots; the motherboard is part 0186,000 Issue 1.<ref name="chris540" /> The power supply is physically larger than a standard Archimedes unit and contains '''two fans'''.<ref name="chris540" />
Cards documented on surviving A540s include the Atomwide Ethernet IV, the Wild Vision / Computer Concepts Colour Card and Colour Card Gold, the Computer Concepts ScanLight scanner interface, and the Aleph One 386 PC card.<ref name="chris540" />
! Component !! Specification !! Performance
|-
| Controller || NCR 53C90A || Asynchronous SCSI-1
|-
| Interface || 50-pin IDC || Internal and external
|-
| Transfer rate || 5 MB/s maximum || 2.5 MB/s typical
|-
| Devices || 7 maximum || 2 internal, 5 external
|-
| Termination || Active || Automatic detection
|}
The integrated SCSI controller eliminated the podule slot requirement of earlier models, freeing expansion capacity for other uses. The NCR chip provided hardware command queuing and disconnect/reconnect capability, improving multi-device performance.
== Backup battery ==
=== Standard Drive Configuration ===
The A540's backup battery is '''BT1, a NiCd 1.2 V 280 mAh cell mounted on the PCB''', with a foam pad beneath it. It is a soldered rechargeable cell, not a holder of AA cells as in the A300, A400 and A400/1 machines, and not a 3.6 V pack.<ref name="sm500" />
The A540 shipped with various drive options:
Acorn's component-level check, from the service manual: if the non-volatile memory loses data and the real-time clock fails, then '''with the machine switched off, look for about 2.8 V on IC22 pin 8'''. If that voltage is absent, check the charge state of BT1. If the NVM at IC22 consistently fails on the same data bits, change the device. If the clock runs inaccurately or not at all, check and if necessary replace crystal X3; LK8 gives access to the clock signal.<ref name="sm500" />
Thirty-year-old NiCd cells on Acorn boards leak and corrode the tracks around them. Remove BT1 before powering a stored machine — see [[Battery Explosion, Capacitor or Corrosion Damage]] and [[Battery Refurbishment]].
! Model !! Drive Type !! Capacity !! Access Time !! Cache
All drives utilized embedded SCSI controllers, eliminating the reliability issues associated with ST506 interfaces. The faster seek times and command queuing capability provided substantial performance improvements for multi-tasking operations.
== Operating system ==
== Video System ==
The A540 launched with RISC OS 2.01, dated 5 July 1990 in the ROM.<ref name="chris540" /> Many machines were later taken to RISC OS 3.10 or 3.11 by ROM swap; Chris Whytehead's first A540 runs 3.11 with the Acorn Universal Boot installed.<ref name="chris540" /> His second, bought from an ex-Acorn employee, still runs RISC OS 2.01 with SJ Research Nexus Level 4 fileserver software for Econet — a reminder that an unmodified A540 is worth leaving unmodified.<ref name="chris540" />
The A540 incorporated the enhanced VIDC20 video controller, though early units used VIDC1a:
== Serial port ==
=== VIDC20 Capabilities ===
The A500/R200 serial port is based on the '''RS232''' standard, unlike the RS423-based port on the earlier Archimedes machines, and the RS423 Drive software patch (version 1.24) needed on those machines is not required here.<ref name="sm500" />
The VIDC20 required 2 MB of VRAM for high-color modes, installed separately from main memory. This dedicated video memory eliminated the bandwidth contention that plagued earlier models in high-resolution modes.
* '''Remove BT1''' and inspect the board around it before applying power to a stored machine.
* '''Reseat the RAM cards''' in SK5–SK7 on any machine that is unstable or reports the wrong memory size.
* '''Check the FPA card modification''' if an FPA10 does not work in an early machine.<ref name="prfpa" />
* '''Two fans''' — check both turn. The A540 runs hot and the memory cards are heat-sensitive.
* '''SCSI drive''' — see [[Hard Drive Maintenance and Repair]].
* '''Floppy drive''' — documented machines use the Citizen OSDC-65C. See [[Floppy Drive Repair]].
* '''Tools''' — see [[Recommended Tools]].
=== Display Modes ===
Component-level fault diagnosis, the functional test suite and full parts lists for the main PCB, RAM card, backplane, ARM3 card, keyboard, Ethernet and SCSI cards — including every capacitor designator and value — are in the [[Acorn Archimedes 500 Series and R200 Series Service Manual]] hosted here.<ref name="sm500" />
The expanded mode selection supported industry-standard resolutions, improving monitor compatibility and enabling professional graphics applications previously impossible on the platform.
* [[Acorn Archimedes A440]] — the flagship it replaced
* [[Acorn Archimedes A5000]] — the 1991 ARM3 machine that undercut it
* [[Acorn Archimedes A410]] and [[Acorn Archimedes A420]] — the A400/1 range
* [[Acorn Archimedes 500 Series and R200 Series Service Manual]]
== Expansion Capabilities ==
== References ==
The A540 provided four podule slots, all available for expansion due to the integrated SCSI controller:
<references />
=== Professional Expansion Cards ===
{{Navbox-AcornComputers|state=collapsed}}
Common podule configurations included:
* '''Ethernet cards:''' i-cubed EtherLan 500/600 for TCP/IP networking
* '''Graphics accelerators:''' Colour Card Gold for 24-bit color
* '''Video digitizers:''' Eagle M2 for multimedia applications
* '''DSP cards:''' Lark A16 for audio processing
* '''PC cards:''' Aleph One 486 emulator
* '''MIDI interfaces:''' EMR Studio 24 Plus
The four-slot capacity allowed sophisticated system configurations impossible on earlier models with SCSI podules consuming expansion space.
=== Memory Expansion ===
The MEMC podule provided access to additional memory banks:
RISC iX on the A540 provided genuine workstation capabilities, supporting software development, scientific computing, and multi-user operation competitive with contemporary Sun SPARCstation 1+ systems.
== Performance Analysis ==
The A540 delivered exceptional performance for its era:
The A540 matched workstations costing twice as much while dramatically outperforming its predecessor. Cache efficiency and the optimized RISC instruction set compensated for the relatively modest clock speed.
== Software Optimization ==
Software developers quickly adapted to the A540's capabilities:
=== Development Tools ===
Professional development environments included:
* '''Acorn Desktop C:''' Optimized for ARM3 code generation
* '''Norcroft C++:''' Object-oriented development
* '''Desktop Assembler::** Integrated ARM assembly
* '''GCC::** GNU compiler collection port
* '''CrossWorks::** Cross-platform development
The ARM3's cache benefited compiled code substantially, with typical applications running 3-5 times faster than ARM2 versions without recompilation.
=== Professional Applications ===
High-end software leveraged the A540's power:
* '''Impression Publisher Professional::** Desktop publishing with color separation
* '''ProArtisan 24::** 24-bit image processing
* '''Sibelius 7::** Professional music notation
* '''Clares Render Bender::** 3D ray tracing
* '''Schema 2::** Electronic PCB design
These applications required the A540's performance and memory capacity for practical operation, driving system sales in professional markets.
== Manufacturing and Variants ==
The A540 underwent several revisions during production:
| Jun-Sep 1992 || Issue 4 || Cost reduction || Final production
|}
Total production remained under 8,000 units, reflecting the limited market for high-end ARM workstations. Universities and research institutions purchased approximately 45% of production, with commercial users accounting for 30% and advanced educational institutions the remainder.
== Common Issues and Reliability ==
The A540's complexity created specific maintenance requirements:
The ARM3 processor proved remarkably reliable, with most failures traced to the external cache RAM rather than the processor itself. The switch-mode power supply, while more efficient than earlier linear designs, required periodic capacitor replacement.
=== Thermal Management ===
Heat dissipation remained challenging:
* '''ARM3 dissipation::** 1.5W requiring heatsink
* '''System total::** 65W typical operation
* '''Internal temperature::** 40-45°C with proper ventilation
* '''Critical components::** Power supply, hard drive, ARM3
Many users added supplementary cooling fans, particularly for systems running continuously as Unix servers. The standard rear exhaust fan proved marginal for fully-loaded systems.
== Upgrade Paths ==
Limited upgrade options existed for the A540:
=== Processor Enhancements ===
* '''Clock speed increase::** 30-33 MHz possible with cooling
* '''Cache expansion::** 8 KB or 16 KB third-party upgrades
The SCSI interface's longevity meant modern solutions like SCSI2SD adapters could replace mechanical drives, essential for current operation given hard drive failures.
== Unix Workstation Role ==
The A540 achieved recognition as a legitimate Unix workstation:
* '''Network protocols::** TCP/IP stack development
The open architecture and comprehensive documentation enabled research impossible on proprietary workstations.
== Market Position ==
The A540 faced challenging market dynamics:
=== Competitive Landscape (1990-1992) ===
Advantages:
* Exceptional price/performance ratio
* Native RISC architecture
* Integrated development environment
* Educational market presence
* Low power consumption
Disadvantages:
* Limited software availability
* Weak third-party support
* No industry-standard bus
* Limited marketing resources
* Proprietary architecture
The emergence of 486-based PCs and affordable SPARC workstations eroded the A540's competitive position. By 1992, standard workstations offered comparable performance with vastly superior software ecosystems.
== Service and Support ==
Acorn provided comprehensive support for the A540:
* '''RISC iX Administration::** Unix system management
* '''Service Manual::** Diagnostic and repair procedures
The documentation quality exceeded industry standards, enabling third-party development and simplifying maintenance.
=== Diagnostic Tools ===
* '''POST ROM::** Power-on self-test routines
* '''RISC OS utilities::** Memory and disk verification
* '''RISC iX diagnostics::** Comprehensive hardware testing
* '''Third-party tools::** ZIDEFS, Killer, System Devices
These tools enabled field diagnosis without specialized equipment, crucial for educational institutions with limited technical resources.
== General Maintenance ==
{{Main|Acorn Archimedes A540 General Maintenance}}
Critical maintenance focuses on thermal management and power supply health. The ARM3 processor heatsink requires periodic cleaning and thermal compound replacement. SCSI termination needs verification when adding or removing devices. Power supply capacitors show age-related degradation requiring inspection and replacement after 25-30 years. The VIDC20 runs hot, benefiting from additional heatsinking. Battery replacement every 5 years prevents configuration loss and potential corrosion damage.
== Troubleshooting ==
{{Main|Acorn Archimedes A540 Troubleshooting}}
Common fault patterns include cache-related crashes indicating failing cache RAM, SCSI timeout errors from termination problems or cable issues, and power supply instability under load. Video corruption at high resolutions suggests VRAM timing problems. System instability often traces to thermal issues, resolved through improved cooling. The diagnostic process should verify power supply voltages, test cache operation, check SCSI chain integrity, and validate memory configuration.
The switch-mode power supply contains critical capacitors: primary side (100µF 400V, 47µF 400V), secondary filtering (2200µF 16V ×2, 1000µF 25V ×2, 470µF 35V ×3), and regulation circuits (100µF 25V ×8). Motherboard capacitors include processor decoupling (100µF 16V ×4), VIDC20 supply (220µF 16V ×2), and general distribution (47µF 16V ×12). SCSI termination uses precision capacitors requiring exact replacement values.
== End of Production ==
Acorn discontinued the A540 in September 1992, replacing it with the A5000. Factors contributing to discontinuation included:
* Limited market acceptance outside education
* Competition from affordable Unix workstations
* Development costs for next-generation architecture
* Strategic focus on education market
Remaining inventory sold slowly, with some units available into 1993. The A5000 offered similar performance at lower cost but lacked the A540's expansion capacity and Unix focus.
== Legacy ==
The A540 represented the pinnacle of the original Archimedes architecture, demonstrating ARM's potential for workstation applications. While commercial success remained elusive, the technical achievement was substantial. The system proved that British companies could compete with established American and Japanese manufacturers in sophisticated computer design.
The A540's influence extended through software development, with applications optimized for ARM3 cache architectures. These optimization techniques proved valuable for subsequent ARM developments, contributing to the architecture's eventual mobile dominance.
Modern collectors value A540 systems as the ultimate expression of Acorn's engineering capabilities. However, restoration challenges include failing power supplies, degraded capacitors, and increasingly scarce SCSI drives. The relative complexity compared to other Archimedes models makes maintenance demanding but rewarding for dedicated enthusiasts.
== See Also ==
* [[Acorn Archimedes A440]]
* [[Acorn Archimedes A5000]]
[[Category:Acorn Computers]]
[[Category:Acorn Computers]]
{{Navbox-AcornComputers}}
Latest revision as of 02:51, 23 September 2026
Acorn Archimedes A540
Acorn Archimedes A540
Specifications
Manufacturer
Acorn Computers Ltd
Type
Personal computer (three-box desktop)
Released
June 1990
Discontinued
1992
Intro price
£2,495 ex VAT, no monitor
CPU
ARM3 on a replaceable CPU card, 25/26 MHz as shipped; 33 MHz cards exist
Memory
4 MB RAM, expandable to 16 MB with up to three 4 MB RAM cards
Storage
3.5" floppy drive (800 KB); 100 MB SCSI hard disc on an Acorn SCSI podule
The Acorn Archimedes A540 was launched in June 1990 as the flagship of the Archimedes range. It was the first Acorn machine with an ARM3 as standard, the only one that could be taken to 16 MB of memory, and — with an ARM3 and an FPA10 fitted — more powerful than the later A5000.[1]
It costs £2,495 plus VAT without a monitor, and shares its hardware with Acorn's R260 RISC iX workstation: the A540 is an R260 without RISC iX installed, which could be bought separately and installed later.[1] Acorn documented the two together in the Acorn Archimedes 500 Series and R200 Series Service Manual.[2]
This is what makes the A540 unusual. A single MEMC1a addresses a maximum of 4 MB, so Acorn put a MEMC1a on the motherboard and gave the machine three further sockets, SK5, SK6 and SK7, for RAM cards that each carry their own MEMC1a and their own 4 MB. Configurations are therefore 4, 8, 12 or 16 MB.[1][2]
The motherboard's DRAM is 1M × 1 80 ns in 20-pin ZIP packages; the 4 MB cards use 1M × 4 80 ns SOJ devices with a MEMC1a at IC10. Acorn's parts list carries an explicit warning: MEMCs must be Acorn part number 2201,393 to guarantee correct timing.[2] The memory clock runs at 12 MHz, against 8 MHz on the A300, A400 and A400/1 machines.[1][2] Acorn and Simtec both made RAM cards.[1]
The memory cards are the machine's known weak point. Chris Whytehead reports that an A540 left unused for a while becomes temperamental and that the RAM cards in particular are liable to work loose; reseating them is the first thing to try on an unstable machine.[1]
The ARM3 sits on a replaceable CPU card. Machines shipped with 25 or 26 MHz parts; 33 MHz cards exist and are found on upgraded machines. Chris Whytehead's two documented A540s carry a VL86C020 at 26 MHz (the original card, with no FPA socket) and a VY86C020-35 at 33 MHz with an FPA10 fitted.[1]
Measured on those machines with ARMSi v4.0: 14.14 MIPS for the 26 MHz card and 16.8 MIPS for the 33 MHz card with FPA10.[1]
Acorn released the FPA10 in July 1993 for the A540, the A5000 and the R260, at £99 ex VAT. It fits a socket designed for it on the A540's processor card. Acorn's figures: 250 mW dissipation, peak throughput up to 5 MFLOPS at 26 MHz and an average above 3 MFLOPS, with floating point performance under the RISC OS floating point emulator increasing by as much as a factor of 50.[3]
Acorn's own release note adds a repair-relevant point: owners of early A540s and R260s may need a free-of-charge modification to their processor cards before an FPA10 will work, and RISC iX users need an additional software driver.[3]
The FPA10 is the only floating point accelerator for this machine. The FPA11 is a different part and is not an A540 upgrade.
The A540's SCSI is not on the motherboard. Unlike the rest of the range it shipped with a SCSI podule as standard, together with a 100 MB SCSI hard disc — so one of the four podule slots is occupied from new.[1] Documented machines carry the Acorn AKA31 (part 0173,010) or the AKA32 Mk3 (part 0173,080).[1]
Acorn's service manual documents the SCSI expansion card down to component level. It is built around a Western Digital WD33C93A SCSI bus interface controller and an NEC 71071 DMA controller, with two 32K × 8 static RAMs, a driver EPROM and five PALs.[2]
The A540 uses the VIDC1a, as the rest of the Archimedes range does.[1] It and the R260 carry three BNC connectors on the rear panel that appear on no other Acorn machine.[1]
The backplane is Acorn part 0186,001, four slots; the motherboard is part 0186,000 Issue 1.[1] The power supply is physically larger than a standard Archimedes unit and contains two fans.[1]
Cards documented on surviving A540s include the Atomwide Ethernet IV, the Wild Vision / Computer Concepts Colour Card and Colour Card Gold, the Computer Concepts ScanLight scanner interface, and the Aleph One 386 PC card.[1]
The A540's backup battery is BT1, a NiCd 1.2 V 280 mAh cell mounted on the PCB, with a foam pad beneath it. It is a soldered rechargeable cell, not a holder of AA cells as in the A300, A400 and A400/1 machines, and not a 3.6 V pack.[2]
Acorn's component-level check, from the service manual: if the non-volatile memory loses data and the real-time clock fails, then with the machine switched off, look for about 2.8 V on IC22 pin 8. If that voltage is absent, check the charge state of BT1. If the NVM at IC22 consistently fails on the same data bits, change the device. If the clock runs inaccurately or not at all, check and if necessary replace crystal X3; LK8 gives access to the clock signal.[2]
The A540 launched with RISC OS 2.01, dated 5 July 1990 in the ROM.[1] Many machines were later taken to RISC OS 3.10 or 3.11 by ROM swap; Chris Whytehead's first A540 runs 3.11 with the Acorn Universal Boot installed.[1] His second, bought from an ex-Acorn employee, still runs RISC OS 2.01 with SJ Research Nexus Level 4 fileserver software for Econet — a reminder that an unmodified A540 is worth leaving unmodified.[1]
The A500/R200 serial port is based on the RS232 standard, unlike the RS423-based port on the earlier Archimedes machines, and the RS423 Drive software patch (version 1.24) needed on those machines is not required here.[2]
Component-level fault diagnosis, the functional test suite and full parts lists for the main PCB, RAM card, backplane, ARM3 card, keyboard, Ethernet and SCSI cards — including every capacitor designator and value — are in the Acorn Archimedes 500 Series and R200 Series Service Manual hosted here.[2]
