1 Topic by cobraguy

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Topic: Cab4n / CM-2 CobraNet cable length

The Cab4n may use Cirrus Logic CM-2 modules instead of CM-1 modules. This is currently the only Peavey product which uses CM-2.
The CM-2 uses a DM9000E MAC/PHY chip  from Davicom. There is a known bug in this chip related to termination impedance which affects the permissible Ethernet cable length. Errors can occur if the cable is too short.  This may result in CobraNet data errors which appear as audio dropouts. This will not occur on all DM9000E devices and the prevalence of this bug has been found to be variable.

Workaround: If using a device which contains a CM-2 module, do not use Ethernet cables on the CobraNet ports shorter than 2 meters. 3 Meters or more is best.

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2 Reply by phils

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Re: Cab4n / CM-2 CobraNet cable length

Is this in all CM-2 CAB4n's from first shipping?
Any idea what errors would show in Disco?
So to confirm, if switch and CAB are in same rack (eg), use 3m cables? Right?

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3 Reply by cobraguy

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Re: Cab4n / CM-2 CobraNet cable length

First, this issue applies to any CobraNet interface that is based on the Cirrus logic CobraNet chips (CA181xx and CS n49622). That includes the CM-2 module that can be used in a CAb-4n. CAB-4n devices have also been manufactured with CM-1 modules. The CM-1 does not have this potential problem.

This issue was first reported about a year ago, is not common and does not exist in all devices. Davicom,  the manufacturer of the MAC/PHY chip used in the CM-2, has confirmed the problem. No qualitative data exists that can be used to identify exactly which devices are suspect.

The problem will show up as audio dropouts, most likely with an error code of 60, 61 or possibly 80.

If your network is working OK then you have nothing to worry about. If you are getting intermittent dropouts AND can see no other reason for this happening AND are using short cables connected to the CobraNet ports of a CM-2 equipped CAB-4N , then try using longer cables.

It must be emphasized that this is not a common problem and that the original posting was made only to insure that, in the event you are having inexplicable dropouts and cannot find the problem, you are made aware that this could be the reason.

If the switch and CAB are in the same rack, then use of three meter cables should insure that this problem does not appear. If you are using shorter cables now and are seeing no problems then you should be OK. This issue does not exist on all devices.

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