Oscilloscope memory depth: confusing terminology - Page 1
Forum section: electronics / testgear

author: djrapp
author_rank: Newbie
timestamp: October 17, 2015, 10:43:43 pm
content: Hi Folks,Forgive me if this is a naïve question--I am trying to understand the terminology surrounding sample memory on oscilloscopes.For most modern oscilloscopes, I see this described in terms of the number of points--for example, the Keysight DSOX2022A specs state "100 kpts standard, up to 1 Mpts optional." However, I recently picked up a used Agilent 54622A which has "4 MB of MegaZoom deep memory mapped to 32 levels of intensity."I am not sure what to make of this spec. Given that the 54622A has 8 bits of vertical resolution, and that only one of the scope's channels is used, meaning that the 2MB dedicated to each channel is interleaved, would this translate to 4 Mpts? Or would each point require 13 bits (8 bits vertical res. + 5 bits for the 32 levels of intensity)? Or something else? Thanks for the advice!

author: tec5c
author_rank: Frequent Contributor
timestamp: October 18, 2015, 01:03:07 am
content: Weren't the 54600 series the first introduction of vectors per second?

author: djrapp
author_rank: Newbie
timestamp: October 18, 2015, 06:23:33 am
content: Yes, I believe so. Seems like they went pretty big on the marketing jargon for that release.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: October 18, 2015, 09:33:41 am
content: Quote from: djrapp on October 17, 2015, 10:43:43 pmAgilent 54622A comes with 4MB sample memory that is halfed when used in two channel mode.4MB means 4Mpts since the scope uses 8bit data points. Sample memory does not store intensity levels (which are made up from multiple samples and are build up in the display memory).

author: djrapp
author_rank: Newbie
timestamp: October 18, 2015, 04:49:28 pm
content: Ah, excellent. Thank you very much!

author: free_electron
author_rank: Super Contributor
timestamp: October 18, 2015, 05:50:32 pm
content: Wuerstenhund is correct.the 546xx Megazoom machines are unique and cannot be compared to most other scopes out there.They have storage for 4 Million sample points ( each point being 8 bit wide ) turn on two channels and it is cut in half.for the 624 or 622D there is additional memory for either chanel 3+4 or the 16 digital inputs.These machines use special processing logic and have a custom graphics processor that can overlay data to create the grayscale ( 32 levels of grayscale) image.Evne though i own much newer and more performant machines i frequently grab my trusty 622D or 645D to debug a mixed mode system. These things are virtually unbeatable when it comes to ease of use and capabilities. you can frequently find them for cheap on ebay.I woudl recommend anyone to pick on of these up.

author: djrapp
author_rank: Newbie
timestamp: October 18, 2015, 09:00:29 pm
content: Thank you both for the advice.free_electron, I'm glad to hear that you're a fan of the 546xx scopes... I snagged the 54622A the other day on eBay without doing much prior research (at $100, it seemed to be significantly below the going rate), and I'm hopeful that between the Agilent and my LogicPort, I'll have my bases covered for the low-speed digital work that I spend most of my time on. Comparing it to modern scopes in the sub-$300 or so range, it seems like it still holds its own remarkably well.

author: PaulAm
author_rank: Frequent Contributor
timestamp: October 18, 2015, 09:30:23 pm
content: I picked up a 54645d as a cheap MSO option and I've been quite happy with it. You can add FFT with a piggyback module. The sampling rate might be a limitation for some work, but it's fine for what I do.The only downside is that it's tough to find one for a reasonable price with the logic pod and the pods by themselves are just crazy. The good news is they were used across a number of instruments and sometimes you can find a 16 bit LA with the pod for cheap (I found one for $50).The only thing that it lacks is serial decode, but if you're cheap, you can't have everything