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HomeTroubleshooting  • Rockwell/Conexnat ACF Chipset

Rockwell/Conexant ACF Chipset  (Updated 13-Mar-06)

The Conexant ACF chipset is used to build a hardware-controller-based modem. This type of modem has flash memory which holds the firmware that makes the modem work. Conexant does not make modems - the chipset is sold to companies that design and build the actual modems for resale to others in the distribution chain or to the end user.

Modems based on this chipset are most often an external with a standard RS-232 serial interface that can connect to nearly any kind of computer running nearly any kind of operating system. (The chipset can and is used in some internal modems as well.) Modems with this chipset need no driver or other special software to operate as a modem. With Windows operating systems, the "driver" is little more than an .inf file defining the commands the modem accepts and the responses the modem returns. The modem will work without any driver in Windows with Hyperterminal as described here. The modem will work with a Windows standard modem (or many other) drivers, although it may not be given the best init string - so it's best to install the modem with the proper driver.

Unlike software-based modems (controllerless - with or without DSP), updating or changing the driver will have absolutely no effect on the modems ability to give you a good, high-speed, problem-free connection. A firmware upgrade for the modem - obtained as a flash upgrade from your modem vendor - may improve (or degrade) connectivity and performance. It is important to get the correct flash upgrade, and that the flash completely finish before turning off the modem or computer: if the flash starts and doesn't complete, or if the wrong flash is used, the modem may become 'dead' - unusable. (See: Who Manufactured My Modem.) 

There are a number of versions of the ACF chipset. The first 56k ACF was introduced before the V.92 and V.90 standards and supported K56Flex; when V.90 was introduced as a standard, these modems did not have enough memory to support both K56Flex and V.90, and could be flashed and flashed-back to support either K56Flex or V.90 at any one time. The current ACF is commonly referred to as ACF2 and has twice as much ROM (2mb vs 1mb). There is also a 33.6k (V.34) ACF chipset, and a new, fourth-generation that may be referred to as ACF3. The new ACF3 allows for a low-cost design as a single chip contains EEPROM, RAM, DSP, controller (CX88168 SCM - Single Chip Modem). The system-side of a solid-state DAA (CX20463 SmartDAA™) is the second chip in Conexant's "SmartSCM device set". Mainpine is reported to be using this design in its multi-port PCI modem cards.

V.92-capable versions also require a software applet to support modem-on-hold: NetWaiting (more info).

Commands to control modulation (enable/disable V.90, K56Flex, V.34, etc.)
Commands to control connect speed limits
If your CONNECT speed is invalid (57.6k, 115.2k, etc.)

Conexant AT Command Reference Manual is available from the Modemsite Download Area.

DIAGNOSTICS: Post-call diagnostics, which can give you a better idea of what's going on with your connection, can be obtained with Hyperterminal using the AT&V1 and/or AT&V2.

ACF2 chipsets: 

(AT) S202 controls certain 56k/V.90 parameters and automatic &V2 response. S202 is bit-mapped, meaning the value for the command S202=# is the decimal sum of the values associated with each of the 8 bit settings (numbered 0 through 7). The default setting for S202 will probably be zero. Here's what you can do:

Bit 4 (S202=16) turns on an automatic AT&V2 response whenever there is a CONNECT or DISCONNECT (and thus will appear in Modemlog).

Bit 7 (S202=128) enables SREJ (selective reject). If the server side modem you are calling supports SREJ (3Com/Commworks, Bay/Nortel), this may be desirable: SREJ eliminates retransmission of correctly received data after an error is detected - only the data in error is re-transmitted.

Bit 1 (S202=2) Enables V.90 digital pad compensation. 

Bit 5* (S202=32) and 6* (S202=64) control the K56Flex and V.90 transmit levels. The default is -12dBm; when the bit is set, it becomes -6dBm. ( -6 being a HIGHER signal level).

To set more than one bit, add the decimal values above for each and enter the sum for # in S202=#.

*Bob Young in Florida reports:

I could not get V.90 to work with a new ISP I am trying, so I tried S202=64, but it did not help. After a lot of experiments, I finally tried S202=32 and - hallelujah! - it worked. I got V.90 at 52000. So it seems that the Flex and V.90 settings on your ACF page are reversed.

(Further experiments would be required forcing a K56Flex connect to determine whether bit 5 or 6 have an effect - see this post by Franc Zabkar indicating bit 5 (K56Flex) settings have no effect, and bit 6 produces a hex dump.)

Beta firmware 3.500 beta 2 for modems with RP56D/SP L2800-38 chip with 2mb flash is available from Modemsite's Download Area. (See note below regarding ACF3 firmware 1.702.11 firmware enhancements that also apply to this release. The Conexant base code was modified and improved by Dmitry Mishchenko (aka Doctor) and Igor Belyanin.

ACF3 Chipset:

Modified firmware, version 1.702.11 for ACorp Speakerphone External modem SC56D is available from Modemsite's Download Area. (Conexant CX-6827-11 chip w/ 2mb Flash.) 

The above files include flashloader for Windows. The Conexant base code was modified and improved by Dmitry Mishchenko (aka Doctor) and Igor Belyanin.

This firmware has some new registers:

  • S202-bit 5 which disables dual-PCM detector and can increase speeds on some lines. 

  • S215 affects dual-PCM. 

  • S216 bit 0 disables -15db server TX level on V.90/V.92; bit 1 disables power drop on V.34. 

  • S17 - bit 1 - controls voice retrain indication ( only)

Mike in Australia reports D-Link DFM-562E uses this chipset. Model he bought, mid 2005 has firmware v1.801 (ACF3_V1.801A-V90_P21_FSH)

(If you have suggestions for info that should be included in this section - let me know!)


Makers of modems with the ACF chipset include:

Amigo Technology Co. Ltd - OEM for various 'brands' including C-net, CenDyne, 3Net
Aztech (MF3850)

Best Data (56SX-92)
Diamond Supra
D-Link (DFM-562E)
Phoebe (CMV1456VQH-2MRA - ACFII)
Zoom (3049C)

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