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Section 2 - Upgrades and Expansion.

 Q2.1) What's the memory limit on current machines?
 Q2.2) What is a second processor and what second processors are there?
 Q2.3) Can PC VGA & Multisync Monitors be added to an Acorn machine?
 Q2.4) Can I connect a SCART monitor to my Acorn machine?
 Q2.5) What was a VIDC enhancer?
 Q2.6) Are there any Acorn cards for IBM PC or compatible machines?
 Q2.7) What configuration of serial cable should I use for modem work?
 Q2.8) How do I make a Null modem cable?
 Q2.9) How can I get unfiltered sound from an Acorn machine?
 Q2.10) What are StrongARM dipswitch settings?
 Q2.11) Are there any PIC programmers available for RISC OS?
 Q2.12) Can you add a TV card to a RISC OS machine?

Q2.1) What's the memory limit on current machines?

The Iyonix computer can have a maximum of 1GB RAM added to it, in the form of two 512MB RAM modules. The Iyonix RAM is 200MHz DDR RAM. The most common configuration of Iyonix machines is 128MB or 512MB.

The A9 Home cannot be upgraded, as it's a sealed unit. It contains 128MB SDRAM and 8MB VRAM.

Information on Risc PC and earlier systems can be found at

Q2.2) What was a second processor and what second processors were there?

A second processor was the generic name for a range of parasite processors that could be linked to Acorn's original 8 bit machines via what was called the 'Tube' interface. Basically the host machine became dedicated to handling the Input and Output while the second processor would do the higher level functions (like running your programs).

The second processor ran asynchronously to the host processor allowing incredible increases in execution speed for programs. A wide range of processors were supported this way allowing Acorn's eight bit range of machines to remain viable and useful for much longer than their technology would suggest.

For more information on legacy second processor systems, see

Q2.3) Can standard PC VGA & Multisync Monitors be added to a RISC OS machine?

All current RISC OS machines and older Risc PCs, come fitted with standard 15 pin 'D-type' VGA connectors for video out, so should work on pretty much all standard monitors, both CRT and LCD flat panel types.

If you have an older legacy machine, additional information and wiring diagrams for connecting VGA monitors is available online at

N.B. The Risc PC can sometimes get confused when set to 'auto' monitortype, resulting in a blank screen and no display on the monitor.

If this happens, try re-configuring the CMOS ram settings to the following and then reseting the machine.

*Configure Monitortype 4
*Configure Sync 0
*Configure Mode 40

These settings should prevent the monitor confusing the auto setting of the Risc PC.

Q2.4) Can I connect a SCART monitor to my Acorn machine?

If you have an older Acorn machine with a nine pin video socket, then yes and here is the wiring diagram :-

[image csafaq/fig3.gif]

A SCART connector is also known as a Euroconnector or a Peri-Television connector.

                Arc             SCART
Ground (0V)     6 -+---------+- 13      Red ground
Ground (0V)     7 -+         +- 9       Green ground
Ground (0V)     8 -+         +- 5       Blue ground
Ground (0V)     9 -+         +- 13      CVBS video ground

Ideally each ground wire should be linked to a separate Arc pin. Also, depending on your SCART monitor, pin 16 may need a +5V input to it. Unfortunately the Arc 9 pin socket does not provide a +5V output so this will have to be sourced from somewhere else.

If you have a newer Acorn machine, with the 15 pin high density video socket then you need this kind of wiring :-

[image csafaq/fig4.gif]

Notice the two resistors. Also notice that the HSync output (pin 13) of the 15-way plug has to be connected to the ID[0] input (pin 11) of the same plug. (Be aware I have no direct confirmation that this wiring works.)

As is usual care must be taken when doing this procedure. Older Acorn machine did not have their VIDC chips fully buffered and unplugging/plugging cables from the video socket while the machine is turned on can cause damage to the video circuitry.

If you want to connect a BBC B computer to a Scart monitor, there are some online wiring diagrams at (previously at

Q2.5) What was a VIDC enhancer?

A VIDC enhancer is basically a clock change for your VIDC. Most Acorns (bar the A540 and newer machines) have 24 MHz VIDC chips installed in them. A VIDC enhancer increases this to 36 MHz allowing much higher resolution screen modes to be displayed on your Arc. (800x600x16 or SVGA standard becomes available.) You do not need one to use a Multisync monitor - the standard VIDC handles that just fine. However having a VIDC enhancer is only really useful if you do have a Multi-sync monitor.

Details on a 'build-it-yourself' VIDC enhancer are available online at

Note a VIDC enhancer is unnecessary and incompatible with the Risc PC (and newer) range of machines.

Q2.6) Are there any Acorn cards for IBM PC or compatible machines?

Yes. Three cards in total :-

ARM 2 processor, 4096k Memory, 8 MHz RAM, Brazil OS.

PC ARM development system
Precursor to Springboard. Hardware functionally identical.

An econet link card for the PC.

However, to the best of my knowledge none of these cards are commercially available.

Q2.7) What configuration of serial cable should I use for modem work?

All current machines, along with all machines since the A5000 have come fitted with a 'corrected' serial port as standard. This newer serial port operates as it should and is directly compatible with standard PC cables.

Some older communications software may not take this in account and assume that you have a cable patched in the manner described at

If you do not use such a patched cable on these 'fixed' serial ports this software will generally fail to work completely. (Usually hardware flow control fails.)

With the advent of the Risc PC and all current machines, a standard PC cable is advised. For details on how to wire up a cable for older machines, visit

If you want to wire a console cable to a Sun Netra/Sunfire server, detailed wiring diagrams are available online at

Q2.8) How do I make a Null modem cable?

For starters you will need soldering skills and the necessary components.

Namely cable, connectors (9 pin female D-type), a soldering iron, solder and the will to use them. All of these items, bar the will, can be found down at the local electronic components store. Assuming you have them all then you will need to decide what kind of machines you are hooking together.

There are three cases and I need to define a few terms.

Archimedes is defined to be A300 series, A400 series (including the /I machines), R140, A540, A3000 (but not the A30x0 machines) and R260 machines.

RiscPC is defined to be both the RiscPC series but also the A5000, A4000, A30x0 & A4 machines. All of these machines have a 'PC Style' serial port that conforms closely to RS232 specifications.

This means that if you are connecting your Acorn machine to a non Acorn machine then generally treating the foreign machine as a RiscPC, in terms of serial handling, will work. There are exceptions, Macintoshes in particular have had non-standard serial ports and may require further research before you can create a cable for them.

The cases are :-

Archimedes to Archimedes

[image csafaq/fig5.gif]

Archimedes to RiscPC

[image csafaq/fig6.gif]

RiscPC to RiscPC

[image csafaq/fig7.gif]

Note that most PC compatible machines have 25 pin D type male ports for their second COM port. You have two options in this case - either re-wire the cable for the 25 pin port or you can buy a 9 to 25 pin converter plug.

Either solution works well. Here are the relevant pins for the 25 pin port :-

  Pin No.  Function
     8       DCD
     3       RX
     2       TX
     20      DTR
     7     GND (0v)
     4       RTS
     5       CTS

Q2.9) How can I get unfiltered sound from an Acorn machine?

All Acorn machines are equipped with a sound filter designed to remove high frequency harmonics from the sound output. However this does cause a muffled feel to the sound as on some machines the filter is a little too excessive and it filters out valid frequencies. Also the filter is optimised for 20.833 kHz output and has less desirable results when the output rate is changed. Accordingly people who do audio work often want to bypass the filter.

On all machines bar the A3000 there is the Internal Auxiliary Audio Connector (usually called link LK3), which can be easily plugged into to provide the unfiltered output. This connector has 10 pins on it and is usually found near the headphone socket on the motherboard. The pins are :-

1 Unfiltered Left
2 Ground
3 Filtered Left
4 Ground
5 Auxiliary Input
6 Ground
7 Filtered Right
8 Ground
9 Unfiltered Right
10 Ground

Simply hook into the Unfiltered outputs.

On an A3000 you need two 10uF 16V ALEC capacitors. Look for chip LM324 (IC39) and hook the capacitors like this:-

Pin 1 --> --|+ |--- Unfiltered Left
Pin 2 --< --|+ |--- Unfiltered Right

The Risc PC & A400 machines have a connector similar to the A5000.

There are several caveats to this procedure. Opening your machine may void your warranty and most definitely should not be attempted if you are unsure of the procedure. Do not unplug/plug the unfiltered audio output while the machine is turned on, by bypassing the filter you also bypass the normal protective circuitry for the audio output.

Finally you will hear higher harmonics present in the audio signal so you will need to connect the signal to a filter of some kind to reduce this extra noise.

Q2.10) What are StrongARM dipswitch settings?

The StrongARM card has a set of dipswitches on it that control the clock speed of the processor.

These can be altered but there are some important caveats to mention first :-

This information is for the original 202MHz StrongARM. The newer 233MHz ones can't be clocked as high, as the base crystal speed is different.

Don't change the links while the card has power. This can result in damage to your processor, always turn your machine off before changing settings.

By default two tracks on the back of the card constrain the card to never go faster than 202 MHz. Cutting these tracks invalidates your warranty, so only do this if you are prepared to replace the card.

The chip is officially rated for 202 MHz, running it faster than this speed can result in hardware damage to the processor and will shorten the chip's lifespan. Again, only do this if you are prepared to replace the card.

If you do cut the tracks remember that the card is a multi-layer one, cutting deeper may sever more tracks than you intended and render the card non-functional.

Without cutting the tracks, the dip switches can be used to slow the processor down from 202MHz to 88MHz if required. Each switch sets one bit making sixteen possible speed settings. This table summarises those speed settings :-

     Switches      |              SA frequency
 1  | 2  | 3  | 4  | Revision J and K | Revision R, S and T
 on | on | on | on |    88.473600 MHz |       85.909080 MHz
 on | on | on | off|    95.846400 MHz |       93.068170 MHz
 on | on | off| on |    99.532800 MHz |       96.647715 MHz
 on | on | off| off|   106.905600 MHz |      103.806805 MHz
 on | off| on | on |   143.769600 MHz |      139.602255 MHz
 on | off| on | off|   151.142400 MHz |      146.761345 MHz
 on | off| off| on |   162.201600 MHz |      157.499980 MHz
 on | off| off| off|   169.574400 MHz |      164.659070 MHz
 off| on | on | on |   191.692800 MHz |      186.136340 MHz
 off| on | on | off|  202.752000 MHz |      196.874975 MHz
 off| on | off| on |   213.811200 MHz |      207.613610 MHz
 off| on | off| off|   228.556800 MHz |      221.931790 MHz
 off| off| on | on |   243.302400 MHz |      236.249970 MHz
 off| off| on | off|   258.048000 MHz |      250.568150 MHz
 off| off| off| on |   276.480000 MHz |      268.465875 MHz
 off| off| off| off|   287.539200 MHz |      279.204510 MHz

The default speeds are shown in bold, underlined.
(Thanks go to Matthias Seifert for this information.)

Q2.11) Are there any PIC programmers available for RISC OS?

Robert Sprowson has produced an application called !PICsuite which caters for PIC programming under RISC OS. There is also a free PIC assembler to download, which has BBC Basic style assembly conventions. Visit for more information.

Q2.12) Can you add a TV card to a RISC OS machine?

The Iyonix machine supports standard PCI expansion cards and Robin Hounsome has written drivers for the Pinnacle Rave PCI TV card using the SAA7134 chip from Philips.

More information and his driver can be downloaded from

Part 1 - Hardware and Operating Systems | Part 3 - Hardware Issues & Compatibility

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 Last edit: 11th Apr 2019 at 1:54am (1900 days ago)

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