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2.10) What are StrongARM dipswitch settings?




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This article is from the comp.sys.acorn FAQ, by Paul Vigay with numerous contributions by others.

2.10) 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 indicated with *'s. (Thanks go to Matthias Seifert for this information.)

 

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