Hi Thanks for the information. However driving the scope is not the problem. I started out as a development engineer on VDU's in the early 1970's. Hence setting up the scope is not an isssue. This paticular problem is only related to the DEP and EXAM funtions. The 8e has a cycle split into parts. DEP or EXAM occur in one cycle. There's a Flipflop (RUN) on the 8330 board that is set in a time period at the beginning of the cycle by the debounced DEP key. The memory address would have been set up manually or auto incremented by a previous DEP. The switch register contents are then transferred to the data bus and the memory signalled to write into the preset address. A signal called stop the clears the RUN flipflop at the end of the cycle. So within one cycle the contents of the switch register (data) should be witten into memory when the DEP key is raised. Only it isn't Rod Smallwood -----Original Message----- From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org] On Behalf Of Dan Roganti Sent: 23 March 2008 18:55 To: On-Topic Posts Only Subject: Re: PDP-8/e Rod, I use both Tek scopes here, a 465 and a TDS410A. Most Tek scopes have the facility to perform a single sweep trigger to detect pulses such as that. However old your Tek scope is, there's supposed to be a button to select between 'Auto' and 'Single Swp' triggering. Also, there is a trigger source selector, this can be set for Chan.1, since your most likely to have one scope probe hooked up already. Then in the same area of the trigger panel there is an arming indicator light. This will let you know the scope is ready to detect a pulse after you set the trigger level--adjusting this to the middle should be good enough. You can also set the Horz sweep to somewhere between 100nsec and 500nsec to get a visual with the brightness turned up alittle more since it will be quick. If the pulse is detected the arming indicator will clear and the trigger indicator will blink just once. You'll have to arm the trigger again by selecting the "single sweep' button to check each signal. hope that helps, =Dan [ Pittsburgh --- http://www2.applegate.org/~ragooman/ ] Rod Smallwood wrote: everything.