Suggestions on pattern generator (and logic analyzer) - Page 1
Forum section: electronics / testgear

author: JPortici
author_rank: Super Contributor
timestamp: January 08, 2018, 06:37:43 pm
content: Hi.I am looking for a digital pattern generator.Specs...I guess 8 channel, 1MSPS may be the bare minimum.It doesn't seem to high a requirement and i could just make one myself with the fist MCU i find laying around, but i'd like not to have to write firmware and computer software...Plus having a standalone unit with its own screen and everything..Ideally i would acquire something from a LA, save it as a csv file or whatever, download the file into the patter generator, set the playback speed and go.Re:LA, i am currently using a DSLogic, works fine but i'd like to have a better "real time" operation...In the continous stream mode it triggers, acquires, send over usb, wait for a couple of seconds than acquire again.I'd like to have more of a scope-like operation, this thing doesn't seem to have an history buffer either..I may convince the boss to replace our current picoscope with a new one, with LA channels. I use the picoscope a lot and using a single unit could be a smart thing. Plus, it should have the "real time performance" i want.Or in alternative, a LA that has a pattern generator? Or an AWG with also a pattern generator? (I know hantek do this, and we could also benefit from a new AWG..)

author: nctnico
author_rank: Super Contributor
timestamp: January 08, 2018, 07:21:04 pm
content: Pattern generator boards for Agilent LAs are cheap and plenty. AFAIK the 16700 or 16900 series are relatively recent.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: January 13, 2018, 09:58:43 pm
content: In my opinion, generic pattern generators are not all that useful.Whenever I have a need for a digital stimulus I just generate some Verilog and program it into an FPGA or CPLD eval board.If it is a serial bus stimulus, I would use a processor board, or just re-use some Verilog code.

author: nctnico
author_rank: Super Contributor
timestamp: January 14, 2018, 06:21:23 pm
content: That is one way but you need to have such a board around and hacking some C code or VHDL/Verilog together may be more cumbersome than creating a pattern. Let's not get into introducing errors every now and then. Also pattern generators typically have an adjustable output voltage setting so they can be used with various logic level types.

author: tggzzz
author_rank: Super Contributor
timestamp: January 14, 2018, 07:39:23 pm
content: A variable output voltage is a two-edged sword, just like a *1/*10 scope probe.There is also the possibility of the pattern generator applying a voltage to an unpowered UUT.

author: nctnico
author_rank: Super Contributor
timestamp: January 14, 2018, 07:57:48 pm
content: The real pattern generators I have seen so far have an output resistor around 50 to 75 Ohms as back termination. That limits the current below damage levels unless you have a really sensitive device.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: January 15, 2018, 12:28:38 am
content: Quote from: nctnico on January 14, 2018, 06:21:23 pmIf all you need is a simple pattern, then a generator would be easier.However, a CPLD / FPGA can react to the DUT and adjust its pattern / behavior accordingly.That's a lot more flexible. The setup time isn't really that bad, once you get the hang of it.

author: JPortici
author_rank: Super Contributor
timestamp: January 15, 2018, 09:47:19 am
content: However, a pattern generator is exactly what i need. I have acquisitions of sets of signals that made the unit misbehave, when i think i have isolated and solved the error i want to play back the pattern to see if the unit behaves correctly.Samplerate is low (1 MS/s max), number of signals is 8 max, so in reality i could make my own "Digital pattern playback device" with the first MCU i find laying around -which i will probably do at some point- but if i don't have to write the firmware, test the firmware, write the computer software to download the pattern and control the unit, test the computer software and just get on with my work it would be better.Only dedicated unit i could find at the moment is the agilent nctnico referred to. probably i can do it with some national devices unit.. i have a couple here in the office but they make it reeeeeeally hard for you to use them if they are more than a couple years old.It seems that there is really no need for these things?Oh, another thing.. This is probably something that could be done in simulation, however for the latest series of PIC18 MPLAB Simulator says "Beta-Core Support" which usually means that i can simulate a routine that only use variables stored in GP RAM with 100% accuracy on the result, but have zero assurance that any action involving the peripherals will work at all

author: 0xfede
author_rank: Regular Contributor
timestamp: January 15, 2018, 10:42:54 am
content: Hello JPortici,may I suggest you a DIGILENT Digital Discovery? It has its own pattern generator (16ch-100MS/s IIRC)and it should be cheap enough.Best,0xfede

author: 2N3055
author_rank: Super Contributor
timestamp: January 15, 2018, 11:04:46 am
content: Digital Discovery will do nicely, but I would suggest putting buffers on outputs if you want additional protection...It will capture and generate, and can import/export to CVS file..It is surprisingly useful little thing... You can also make custom logic functions and decodes ...Take a look at the documentation..Regards,Sinisa

author: hli
author_rank: Frequent Contributor
timestamp: January 15, 2018, 11:04:58 am
content: Quote from: 0xfede on January 15, 2018, 10:42:54 am+1 for the DDD. It can store recorded data, though I never tried to replay it later.

author: JPortici
author_rank: Super Contributor
timestamp: January 15, 2018, 11:48:24 am
content: Quote from: 0xfede on January 15, 2018, 10:42:54 amof course. how could i miss it.. thanks fedequick questions related to the LA part:- Can it trigger from serial protocol?- Can it trigger on serial protocol errors?- Can it do both on custom protocols?

author: 0xfede
author_rank: Regular Contributor
timestamp: January 15, 2018, 12:02:29 pm
content: I don't have one but it seems that can trigger serial protocol.There is a thread here for the DDD where you can find many answer:https://www.eevblog.com/forum/testgear/digilent-digital-discovery/I don't know if it is a limitation but the maximum output voltage for pattern generator is 3V3.Best,0xfede

author: 2N3055
author_rank: Super Contributor
timestamp: January 15, 2018, 03:48:06 pm
content: Quote from: JPortici on January 15, 2018, 11:48:24 am1.- Yes. SPI, I2C, I2S, 1Wire, SPI, UART, CAN2.- SPI (Start, Stop, Value), I2C (Start, Stop, any NACK/ACK, Address&Data), I2S (Left, right, data) , 1Wire (Reset, Value), UART (Break, Idle, Value), CAN (Error, Break, Identifier)3.- It can do custom protocol. Don't know about trigger.Regards,Sinisa

author: hli
author_rank: Frequent Contributor
timestamp: January 15, 2018, 07:20:25 pm
content: Quote from: JPortici on January 15, 2018, 11:48:24 amYesQuote from: JPortici on January 15, 2018, 11:48:24 amYesQuote from: JPortici on January 15, 2018, 11:48:24 amUnfortunately no, custom protocols are only used for 'rendering' the result data. But I think the first two capabilities already set the DDD apart from many other, even more expensive, logic analyzers.