AB Connector Tutorial

Introduction:

This article affects customers employing a 6U CompactPCI Rear Panel I/O solution, such as our ZX470 series Fast Ethernet adapter. By industry standards, 6U Rear Panel I/O transition modules (RTMs) use some, or all, of the top 3 connectors for transmission of data from the front to the rear of the chassis through a midplane (see figure 1).

The Problem:

The RTM is a very shallow printed circuit board that "wobbles" or "rocks" when inserted into the chassis. This often causes misalignment of the pins on RP5 with the RJ5 female connector on the RTM. It is easy to force the RTM in while the pins are misaligned, causing bent pins, whole slots to go bad, or in a worst-case scenario, destroying the entire CompactPCI system. The standard connector for RP5 and RJ5 is a "B" type, which has no guide-pins to help align the insertion.

The Solution:

A newer type of connector is called the "AB" connector; it has the same pin-outs as the B connector but it also includes plastic guide-pins. Many CompactPCI chassis manufacturers now use these "AB" connectors for the midplane RP5 connector. Major manufactures such as: Sun Microsystems, Motorola, and AG Communications already use the AB connector. This creates a "good-news, bad-news" scenario:

The Good News:

Any CompactPCI chassis with an AB connector at RP5 will accept an RTM with either the older B style connector or the newer AB connector.

The Bad News:

Any CompactPCI chassis with the older B connector at RP5 will only accept an RTM with the older B style connector. It will not accept a Rear Transition Module with the newer AB connector!

What You Should Do:

Because customers have requested a solution, ZNYX has begun to include the newer "AB" standard connector on its rear transition modules. Therefore, the customer must be able to identify which connector is on their chassis and order the corresponding connector on their RTM.

Below we have included some pictures to better illustrate the problem, the solution, and guide you in ordering the correct rear transition module.

All About AB Connectors:

Figure 1

A typical CompactPCI chassis with Rear Panel I/O capability includes the front-loading peripheral (e.g. a ZNYX ZX478), a midplane/backplane, and the rear transition module (ZX408). When the RTM with the 'B' style RJ5 connector is inserted, it does not have the guide pins to correctly align with RP5. If the board tilts during insertion, the pins on RP5 will be bent.

The Type B Connector:

To the right is an example of a Type B Connector. In the above illustration, this would be RJ5, and would be installed on an older Rear Transition Module. Notice the straight edges.

Figure 2

To the right is an example of a Type B feed thru connector. This is the mating connector with the one shown above, and it is located on the back side of the midplane (RP5). This feed-thru contains 110 pins, or signal contacts.

Figure 3

When a RTM board with type B connectors is replaced without a great deal of care, this is what happens when RJ5 misaligns with RP5: The RP5 pins are bent.

Figure 4

Even if you could straighten out the pins on RP5, this bad insertion attempt may have caused more insidious damage to the other mating connector. Below are photos of actual damage we have observed to the RJ5 connector on our early "B" connector-equipped ZX408 RTM boards. In fact, the bent pins pushed pieces of the plastic connector housing into the pin holes, plugging them up. If this damaged connector is plugged into another slot, it, in turn, the plugged holes bend the pins in that slot.

Figures 5 & 6

The Type AB Connector:

	On the left is an example of the Type AB connector. The arrow points to the guide-pins located on either side of the connector assembly.
	This is an example of a Type AB shroud (minus the 110 signal contact pins). The arrow points to the guide shaft located in the inner part of the shroud. The guide pins mate with this guide shaft. Figure 8

When a CompactPCI chassis and the RTM are both equipped with the AB connector, there is no chance of misalignment, and no damage is incurred, even when performing hasty hot-swaps.

If the midplane/backplane of the CompactPCI chassis has an AB shroud connector and the RTM has a B connector, they will still properly mate, but since there are no alignment pins, the same extreme care should be taken to insure the RTM is properly aligned before pushing the module in the last centimeter of travel.

But, remember, the type B shroud on the CompactPCI chassis will not accommodate a Type AB connector on the RTM.

What Should The Customer Order?

The rear transition modules (RTMs) for the ZX474 or ZX478 adapters are available with either B or AB connectors.

Hub or Adapter?

When connecting a CompactPCI system using a ZX470 series adapter to a hub or switch, use a standard Cat 5 Ethernet cable. If there is another adapter (instead of a hub/switch) at the other end, then use a crossover Cat 5 Ethernet cable to connect them together. Use table 1 below to select the correct model for your application.

Note: All shipments of ZX4004 or ZX4008 RTM's will, unless specified, be with AB connectors

Front Module	Rear Transition Module	Fast Ethernet Channels	RJ-45 connectors wired as an	CompactPCI Connector Type
ZX474	ZX4004A	4	Adapter(MDI)	B
ZX474	ZX4004AB	4	Adapter (MDI)	AB
ZX478	ZX4008A	8	Adapter (MDI)	B
ZX478	ZX4008AB	8	Adapter (MDI)	AB

Table 1

If you have further questions concerning this issue, please contact: your appropriate sales person or you can direct your email to: sales@znyx.com or 510-249-0800.