Similarity of 11000-series interface and 7000-series interface

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Questions to John Addis:

  1. To what extent do 7A-series plug-ins work in 11000-series mainframes?
  2. To what extent do 11A-series plug-ins work in 7000-series mainframes?

Answers from John:

The short answers to your two questions are:

  1. not at all
  2. not at all

The reasons for this are many.

Neither plug-in can be physically fully inserted into the other series’ mainframe. The reason for this is that the connectors at the rear have different projections at the top of the connector. The 7000 series has a short, wide and thick projection and the 11000 series has a long, narrow and thin projection. Neither projection performs any electrical function and it is possible to mechanically remove the part which extends beyond the base of the connector.

The 7000 series projection contains four atavistic holes which were once going to hold SMB connectors for the signal and trigger paths. They were designed into the interface at an early date. Roy Hayes (3A3, 3A8 and 7A12 designer) then suggested that an edge connector could be made with adequate HF response and that the connectors and cables would be an unnecessary expense. The SMB connectors were never used.

The projections can be easily removed with a Dremel tool, allowing mechanical compatibility. I know of no electrical harm from this, but I am not guaranteeing it.

The 7000 series fixed and flexible extenders can also be modified using a Dremel so that 11000 series plug-ins can be trouble shot in 11000 series mainframes. I have done this to a flexible extender. However, you cannot calibrate the 11000 series plug-ins in the 11000 series mainframes when using the 7000 series flexible extender as there are several wires not present in the extender which the 11000 series plug-ins need. I do not know if this is true for the fixed extender.

The rear connectors contain 38 contacts on each side of the board in both 7000 and 11000 series instruments. The top contact on the left side (seen from the front panel) is A38. The last contact on the bottom left is A1. On the right side, the contacts are B38 down to B1 at the bottom. Not all of the contacts of either series were ever used. The contacts for power supplies and signals are the same with the exception that the 11000 series has extra plug-in “aux trigger out” contacts, one pair for each of up to 4 channels. In the 7000 series, these connectors were used for the on screen readout.

  • A38 is ground and B38 is + CH1 aux trigger out.
  • A37 is ground and B37 is − CH1 aux trigger out.
  • Etc
  • A31 is − CH4 aux trigger out B31 is ground.

A37-A30 and B37-B29 are used for the display of plug-in readout information in the 7000 series

A20 and B20 are differential trigger inputs to the plug-in in 7000 series (not sure these were ever used).

In 11000 series, A20 is a serial data interface for mainframe to plug-in information. B20 is an “11000 series detector” tied to +5 V through 10 kΩ in 11000 series.

A21 in 11000 series is serial data clock, B21 is plug-in to mainframe serial data interface while these appear to be unused in the 7000 series.

There are other differences in the interface connector.

Aside from that, the 11000 series plug-ins have no front panel controls except for a single On/Off push button. Without a serial data interface you cannot control plug-in functions (V/div, Coupling, Offset, Bandwidth) in a 7000 series mainframe. The 7000 series plug-ins have front panel controls, but you have to find a way to turn the Left, Center, or Right 11000 series digitizers on so they will display the 7000 series plug-in signals. I have never tried this.

Furthermore, the 11000 series plug-ins cannot be calibrated in 7000 series mainframes.

The way self calibration works in 11000 series is that the mainframe tells the plug-in when it needs to be calibrated. The plug-in then sends requests for a series of accurate voltages and the measured results are returned by the mainframe. The requested voltages are frequently signals that run over a range of 32 bits of the mainframe’s digitizer in a sawtooth (to provide an accurate average signal). A large number of these signals and measurements constitute the information which the plug-in uses to create calibration constants. The calibration constants set voltages in the plug-in which make the plug-in perfectly calibrated. The plug-in also corrects for the mainframe’s imbalance in the calculation. It can do this because the plug-in puts out a reliable zero volts to the mainframe when the channels are all “OFF”. The entire calibration routine comes from the brilliant mind of Brian Rhodefer.

These calibration constants (“cal constants”) are stored in the plug-in’s NVRAM along with other data such as any probe serial number, and probe cal constants (if any) and the plug-in’s serial number. The latter so that the mainframe knows whether that plug-in was there when last calibrated. Lifetime of the battery operated NVRAM, specified as working for 10 years minimum, is typically over 25 years. When it fails, the plug-in must be calibrated every time the instrument is turned on, and it does not come on in the same state as it was when it was turned off.

The 11000 series plug-in is perfectly calibrated except that it also has the mainframe’s input offset built into the plug-in calibration constants.

My advice is that attempting to modify either the 7000 series or 11000 series plug-ins to work in the other series mainframe is not even close to being worth the effort.