Good clues here.
My scope does have the ctt and word options, with the connector mentioned. Is there any hint about where the components you mention are located? On an existing board or an added board?,
Thanks very much. Doug
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--- In TekScopes@..., David Garrido <d.garrido@...> wrote:
Here is a little more on the Theory of Operation of the EXT REF:
"The External Frequency Reference signal, input through the EXT REF (the same physical connection as the WR OUT), comes in through the high pass filter formed by C6180 and R6181. This high pass filter eliminates any DC offset of AC hum that might be present on the incoming reference. R6182 acts as a base current limiter as well as providing partial line termination. Since R6182 is connected to ground only through diodes, the termination impedance is nonlinear and noticeable distortion of the external reference signal is to be expected. This distortion should not affect the frequency content of the reference and hence should not affect the accuracy of any measurements.
Q6180 with R5991, R5992, R6127, and R6183 acts to convert the external reference input signal to a compatible signal. This logic signal appears on the input to the mux U6070. This is the same signal input as the WORD signal from the Word Recognizer. All frequency measurements of the external reference are made using the same CTT setup as would a frequency measurement of the Word Recognizer.
Q6181 is used to turn off the External Frequency Reference input for any mode that does not use the external reference. This allows the Word Recognizer to operate even though it and the External Frequency Reference share the WORD line. While the External Frequency Reference is in use, the Word Recognizer control register is loaded so there can never be a match on the WORD line between External Frequency Reference and Word Recognizer. This insures the Word Recognizer will not conflict with the External Frequency Reference signal in the use of the WORD line."
Hope it helps!!!
