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ACA1221ec is an accelerator for the A1200 computer. It is also compatible with the ACA500 and ACA500plus. Key features are:

  • processor: MC68ec020-25 (few cards have a 16MHz CPU)
  • two clock ports
  • 9 MBytes 32-bit fast RAM
  • 1 MByte Maprom option
  • 6 MBytes usable as RAM disk
  • variable clock speed


jumper settings

The ACA1221ec comes with the "Maprom" jumper closed. In this position, the physical Kickstart ROM will be copied to the 1 MByte memory space for faster execution of all ROM routines. This will significantly improve performance of your system.

Jumper position "unprotect" is only required for flashing the card or changing it's startup speed. This jumper setting will completely disable any setting that you have made using the flash/config tool, so if you have chosen a too-high overclocking speed, this is your "safe setting". Note that only 1MByte of Fastmem is available in this jumper setting!

clock ports

ACA1221ec with expansions

The ACA1221ec features two clock ports for adding hardware expansions. The first clock port is mainly meant for an RTC module. As opposed to earlier accelerators with an RTC port, this port is a straight copy of the internal clock port of the A1200. That means you can also use it to connect a Catweasel MK2, Silversurfer or Delfina card. In that case, the internal clock port of the A1200 may not be used for such an expansion, but can be used for an RTC module. This male clock port is extremely useful if you own an early A1200 mainboard that has the clock port assembled in the wrong position.

Note that if you want to use the internal and the ACA1221ec male clock port at the same time, you may only use one RTC module and one clock port expansion card, but you can never use two RTC modules or two clock port expansions at the same time.

The second clock port of the ACA1221ec is independent of the internal clock port or the male clock port. This means it can be used in addition to any clock port device and/or RTC that occupies the other clock ports. The female clock port has been designed for the RapidRoad USB host controller. A clock port cable is not required; the card must be pluged directly to the ACA1221ec as shown in the picture. A polarity "nose" helps avoiding connection mistakes. For passing power to RapidRoad, the white power output of the ACA1221ec can be used.

If you already have a RapidRoad inside your A1200, we recommend to use this dedicated port instead, as it is considerably faster than the "normal" clock port: You will get over 1MByte/s performance from USB mass storage devices, if the ACA1221ec is running at 28.38MHz.

The second "female" clock port uses memory address 0x00d90001.

startup behaviour

The ACA1221ec can be launched at a speed of your choice. The card comes from the factory configured for the highest guaranteed CPU speed; this is 28.38MHz in most cases. Rare versions with a 16MHz CPU are configured for 17MHz operation at the factory. If the "unprotect" jumper is set, the card will launch at 17MHz, regardless of the installed processor.

clocking and overclocking

The ACA1221ec starts up at it's slowest speed of 17.025MHz. After Autoconfig operations have been completed, the CPU clock will be set to what you have configured, and caches will be enabled. This has been implemented in order to give harddrives enough time to spin up and be available after a cold-start, even under Kickstart 3.0.

For future releases of the tools, the ACAclock tool and the ACAgov CPU governor can set speeds dynamically.

precise clock rate calculation

The ACA1221ec uses a base clock of 85.12548MHz. This clock always drives the SD-RAM controller of the card. The four different CPU clock rates are generated by dividing this clock by the following values:

5: 17.025096 MHz

4: 21.28137 MHz

3: 28.37516 MHz

2: 42.56274 MHz

Please note that although the 28MHz frequency may look like the card is clocked syncronously to the A1200 mainboard (because it's the same as the chipset base frequency), the two clocks are not syncronized at all. The ACA1221ec is a purely asyncronous card, and will run at the exact shown frequencies, even if the host computer is an NTSC version, which is usually clocked at 28.63636 MHz.


For the ACA1221ec and all versions of the ACA1233n, there is a new combined GUI and command line tool available, ACAtool.

Acatool unifies most functionality of the ACA12xx libraries and command line utilities (with the exception of ACAGov) under a single program that can be used from Workbench, command line and startup-sequence alike. It can save the configuration into the ACA1221ec's flash memory and thus also replace the ACA1221ecFlash utility.

ACA1221.library, ACAClock, ACAGov, ACAMapROM with developer docs and sources: ACA1221V1 2Beta1.lha

Flash/Config tool and the ACAname tool for displaying the name of your card: ACAname and ACA1221ecFlash


The ACA1221 instruction sheet can be downloaded here: English/German instruction sheet

Hardware Register Documentation is available for developers.

possible required board modifications

Commodore and Escom have made all kinds of mistakes when assembling A1200 motherboards. Internal memos from Commodore are available that clearly say to remove capacitors E123C and E125C for any version of the Budgie chip, yet, you can find lots of boards out there that have these capacitors assembled. Less often, but at least as severe, some boards have capacitors E121C and E122C assembled. This will harm the quality of the 14MHz board clock to a degree where most accelerators (not just ours!) become instable.

You cannot tell from the board revision or the year of your board if the capacitors have been assembled, as practically all revisions have been assembled with all combinations of chipsets and timing fixes (required or not). Your only chance is to check your individual board and remove the capacitors if they are there. There is no reason for these parts to be assembled, other than some Commodore employee's excuse about not getting the memo.

Only our latest accelerators ACA1233n, ACA1221ec and ACA1221lc have implemented special logic that can handle most of the timing errors caused by wrong assembly of the A1200 main board. These cards may work reliably, although the mentioned capacitors are installed. We still recommend to remove the capacitors, as they have other negative effects, too.

ACA 12xx Benchmarks

Benchmarks are measured with AIBB and the popular Sysinfo tool. While AIBB gives detailed information about the performance in specialized cases, Sysinfo will only give you a rough estimation of the performance you can get. We recommend to download the AIBB modules and compare the specific test results against your machine - this will give you much more information about a certain strength or weakness of the card you're comparing. Fastmem performance is measured with the freely available tool "Bustest". Only the "read multiple" and "write multiple" values are given here. Results may vary due to cache alignment differencies. Starting with the ACA1234, Bustest version 0.19 was used - the previous version was obviously too generous for some tests; take older measurements with a grain of salt.

Product name Sysinfo Dhrystones AIBB module download Fastmem included Fastmem performance r/w Chipmem performance r/w MMU comment
ACA1220-16 3320 media:AIBB_ACA1220-16.LHA 128 MByte 11.8 / 17.7 MB/s 4.2 / 4.5 MB/s no discontinued per apr-2014
ACA1220-20 3998 media:AIBB_ACA1220-20.LHA 128 MByte 14.2 / 21.3 MB/s 4.7 / 5.1 MB/s no
ACA1220-25 4266 media:AIBB_ACA1220-25.LHA 128 MByte 17.6 / 21.4 MB/s 6.1 / 7.0 MB/s no
ACA1220-33 5712 media:AIBB_ACA1220-33.LHA 128 MByte 23.6 / 28.8 MB/s 6.3 / 7.0 MB/s no
ACA1220-40 6867 (n/a) 128 MByte 28.3 / 34.5 MB/s 6.4 / 7.0 MB/s no not officially sold (overclocked)
ACA1232-20 4553 (n/a) 128 MByte 13.3 / 21.3 MB/s (not tested) yes
ACA1232-25ec 5708 media:AIBB_ACA1232-25.LHA 128 MByte 16.6 / 26.7 MB/s (not tested) no
ACA1232-25 5708 media:AIBB_ACA1232-25.LHA 128 MByte 16.6 / 26.7 MB/s (not tested) yes
ACA1232-33 7529 media:AIBB_ACA1232-33.LHA 128 MByte 22.2 / 35.7 MB/s 6.2 / 7.0 MB/s yes
ACA1232-40ec 9045 media:AIBB_ACA1232-40.LHA 128 MByte 26.7 / 42.9 MB/s 6.4 / 7.0 MB/s no
ACA1232-40 9045 media:AIBB_ACA1232-40.LHA 128 MByte 26.7 / 42.9 MB/s 6.4 / 7.0 MB/s yes
ACA1233-40 9045 media:AIBB_ACA1232-40.LHA 128 MByte 26.7 / 42.9 MB/s 6.4 / 7.0 MB/s yes
ACA1232-50 10576 media:AIBB_ACA1232-50.lha 128 MByte 29.3 / 43.6 MB/s 6.4 / 7.1 MB/s yes limited edition, starting mid-November 2015
ACA1233-55 11747 media:AIBB_ACA1233-55.lha 128 MByte 32.6 / 48.4 MB/s 6.4 / 7.1 MB/s yes limited edition, starting mid-November 2015
ACA1221-9.46 1878 media:AIBB_ACA1221-9.lha 9-63 MByte 6.7 / 10.1 MB/s 3.4 / 3.9 MB/s no under-clocked
ACA1221-17.03 3408 media:AIBB_ACA1221-17.lha 9-63 MByte 12.1 / 18.4 MB/s 4.8 / 5.4 MB/s no
ACA1221-21.28 4266 media:AIBB_ACA1221-21.lha 9-63 MByte 15.2 / 23.0 MB/s 6.1 / 6.9 MB/s no overclock option 5,- EUR
ACA1221-28.38 4914 media:AIBB_ACA1221-28.lha 9-63 MByte 20.2 / 30.7 MB/s 6.2 / 7.1 MB/s no overclock option 15,- EUR
ACA1221EC-42.56 6401 (TBD) 9+1+6 MByte 25.8 / 37.1 MB/s 6.4 / 7.0 MB/s no overclocked
ACA1221EC-21.28 4279 (TBD) 9+1+6 MByte 15.2 / 23.1 MB/s 6.1 / 6.9 MB/s no
ACA1221EC-28.38 4926 (TBD) 9+1+6 MByte 20.3 / 30.7 MB/s 6.2 / 7.1 MB/s no
ACA1221EC-17.03 3416 (TBD) 9+1+6 MByte 12.2 / 18.4 MB/s 4.3 / 4.8 MB/s no
ACA1233n-26.67 6031 media:AIBB_ACA1233n26.lha 128 MByte 19.2 / 38.2 MB/s 6.1 / 7.1 MB/s yes
ACA1233n-40 9203 media:AIBB_ACA1233n40.lha 128 MByte 28.8 / 57.4 MB/s 6.4 / 7.1 MB/s yes
ACA1233n-55 11763 (TBD) 128 MByte 35.2 / 50.2 MB/s 6.4 / 7.1 MB/s yes includes A1200 IDE accel
ACA1221LC-20 4015 (TBD) 11.2 MByte 14.4 / 21.7 MB/s 5.9 / 6.9 MB/s no includes A1200 IDE accel, starting dec-2019
ACA1221LC-26 5365 (TBD) 11.2 MByte 19.2 / 29.0 MB/s 6.1 / 7.1 MB/s no includes A1200 IDE accel, starting dec-2019
ACA1221LC-40 7430 (TBD) 11.2 MByte 26.4 / 43.4 MB/s 6.3 / 7.1 MB/s no overclocked, not guaranteed
ACA1234-25 5735 media:AIBB_ACA1234.lha 128 MByte 15.9 / 35.4 MB/s 6.2 / 7.0 MB/s yes
ACA1234-33 7583 media:AIBB_ACA1234.lha 128 MByte 21.0 / 47.3 MB/s 6.3 / 7.0 MB/s yes
ACA1234-40 9193 media:AIBB_ACA1234.lha 128 MByte 25.5 / 58.0 MB/s 6.3 / 7.0 MB/s yes
ACA1234-50 10579 media:AIBB_ACA1234.lha 128 MByte 29.4 / 54.8 MB/s 6.3 / 7.0 MB/s yes



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