Products > Test Equipment
Advice on determining a logic analyzer for use with 1980s synthesizers. TLA715?
TomKatt:
FWIW I was playing around with my DSlogic LA today and noticed that it has a full Z80 decoder available. You might have to play around with triggering options as discussed above, but you can capture and filter addresses, data R/W etc pretty easily. With the large memory ability provided by streaming capture, you could easily analyze the startup process to verify proper operation.
Just figured I’d mention that as it seems like it would be helpful for working on that type of gear. I see that the OP wants a stand-alone device, so prefers a non usb LA…. But if the tool works for the task I don’t see how that applies to the issue? A stand-alone device is basically the logic hardware with a self contained processor running the box, so what difference would it make if the logic hardware and processor were separate devices? Surely there’s no lack of laptops available to make a dedicated usb LA setup? That’s basically what I do - a cheap older tough Thinkbook makes a good addition to my bench. In addition to running my LA, it also connects to my power supplies, scope, and meters for data logging. It’s a tool like everything else.
Edit - looked up the HP 16500.. very impressive. But obviously bench space is not the limiting factor if you’re looking at gear that size lol.
sku_u:
Thank you everyone for replying. There is a lot of invaluable information in here and a lot of points that I would have not considered if it wasn't for your comments.
Some of the key points I've taken away
-LA should be wide enough for all of the address, data, & control lines
-Triggering options
-Capture depth
I am going to inspect the TLA715 this week. I may be able to get this unit fairly cheaply and I may pull the trigger on it if the price is right and it's in good nick unless anyone thinks it would not be a good fit
--- Quote from: tggzzz on June 15, 2024, 09:14:51 am ---When debugging/repairing equipment of that age:
* measure Vcc voltage and ripple, using voltmeter and scope
* use scope to verify signal integrity. 100MHz is sufficient, but be aware of the ringing caused by a 6" ground lead
* thereafter use a logic analyser
--- End quote ---
Some excellent pointers there along with other fantastic advice in your post!
--- Quote from: artag on June 15, 2024, 09:17:52 am ---There are lots of options in terms of digital and analogue capture. Get the deepest memory you can afford but be aware you'll sometimes limit the capture to keep the display time down. On these parallel bus processors you'll be using it in state mode though, which is far more efficient for memory use. There is an analogue scope option. It's often pricy and is very poor compared with modern scopes, but having it in the same box with time-aligned displays and cross triggering is very powerful on a mixed-signal device like a synth.
If you have no prior experience of logic analysers I'd actually recommend doing the same thing. A 1630 (1630D for mixed signal, 1630G for software development) is very cheap and is explained in terms that makes it very comprehensible to a hardware engineer. Later models lacked that straightforward explanation and wrote the manuals in terms of usage examples. IMHO this denies you the basic understanding of what's going on that proper understanding requires. Once you start to suffer from it's limitations, replace it with a more modern one. But your synths were designed by people using that class of analyser - upgrading to a '90s machine is the lap of luxury, adding small probes, deep memories, bigger / better displays.
--- End quote ---
Thank you very much. I had not considered cross-triggering but it seems like a very useful tool to have available. Thank you for mentioning the HP 1630. I really enjoy learning about the kinds of tools and developmental processes the engineers of these synthesizers would have used back in the day. They appear to be fairly inexpensive so I will definitely pick one up in the future!
--- Quote from: MarkL on June 15, 2024, 02:24:26 pm ---The Agilent 16702B is a modular LA with 5 slots and lots of parallel capacity (typically 68 channels per slot) and captures in state or timing mode. You can also get scope cards with limited points (32k) that allows correlated capture with the digital inputs which is useful for checking signal integrity.
Capture cards using the "40-pin probing system" are available with anywhere from 512k to 64M points, amd hacks have been discovered to configure a card to its maximum capabilities. TTL, CMOS, ECL, and custom -6V to +6V threshold levels are supported.
Z80 and other processor decoders are available. Support for modern serial protocols, such as SPI and I2C, is non-existent, although of course it will show you the waveform. Included in the OS is development software, so you can write your own decoders and disassemblers, if so inclined.
If you want something a little smaller, the 1670G and friends is a good compromise, but doesn't provide an accessible OS like the 16702B. It uses the same 40-pin probing system, as does many other from HP/Agilent units from this era.
The 1630 series was mentioned above. I had a 1631D for years, and the triggering was very sophisticated and easy to use. But I found its capture memory of only 1024 points to be extremely limiting.
--- End quote ---
Thank you for chiming in about the 16702B. I wasn't aware of the Z80 and other processor decoders out there!
--- Quote from: TomKatt on June 15, 2024, 02:38:51 pm ---What frequency do these vintage instruments run at? I’d guess many are Z80 or similar running around 4MHz or so.
--- End quote ---
Usually these early 80s synthesizers have 2 processors; one is the key assigner that handles scanning the keybed and the other is the programmer which scans the front panel I/O and is in charge of saving and recalling patches (sounds). Usually they work independently of each other. The Juno-106 uses 2 NEC 7811s, which is a Z80 derivative, as its programmer & key assigner running at 12MHz each. Later Roland synths like the JX3-P use an 8031. The Korg PolySix uses a 8048 & 8049 both @ 6 MHz and the Poly-61 uses 2 8049s at 6 MHz. Interestingly the Korg SP-80's (1983) oscillator design is very similar to the Poly-61 (1982) using 8255s and 8253s to generate square waves, but the SP-80 uses an NEC D780C, a Z80 derivative. There is an 8MHz crystal on the SP-80 board but I believe it uses some circuitry to divide that clock down, but it's been a while since I've looked at it. The SP-80 looks like it was designed in 1980 based on the design of some of the circuit boards inside of it. Ensoniq, an American synth manufacturer, used 6800 derivatives almost exclusively in all of their synthesizers. The ESQ-1 uses 2 6809s with its main programmer running @ 8MHz.
--- Quote from: nctnico on June 15, 2024, 03:53:03 pm ---
--- Quote from: sku_u on June 15, 2024, 08:17:48 am ---A Tektronix TLA715 is available locally and I am considering this unit but I basically know nothing when it comes to the probes and adapters I need. It has two of the TLA7N4 (2GHz timing, 64k) modules installed and comes with several of the P6434 probes. Of course these probes are the ones with the Mictor connector and are of no use to me unless I buy or make a Mictor to 2.54mm adapter. I need help determining which probes would be most suitable for my application and I have allocated several hundred dollars for obtaining these probes. According to the pdf, "Tektronix P6400 P6800 P6900 Logic Analyzer Probes" from https://w140.com/tekwiki/wiki/P6434, it looks like most of the probes are compatible with TTL & CMOS levels. I need some sort of flying lead that can be attached to the pins of chips. I have made a little DIP-14/16 breakout PCB with 2.54mm pin headers that I can attach a probe to as well. The P6417 and P6418 appear to be something I can use but I would like to confirm.
--- End quote ---
I have a TLA715 myself and so far I've been very happy with it (its my 4th logic analyser). A newer model is the TLA7000 series which can use the same modules.
Having a mictor to flying leads adapter is one way to go. I have made something like that a long time ago.
If you want to hunt for flying lead probes, make sure to get the P6417. These are the older model which has tongue shaped contacts which will grab on thin wires as well.
I see some mentioning getting USB logic analysers but I don't think these are very handy as these don't have the elaborate trigger and storage qualifiers a real logic analyser has. What the TLA715 can do is store only when a signal changes. This means A) you can use read/write strobes, chip selects, etc to get a list with addresses a microprocessor is accessing and thus trace which memory locations are accessed B) you need far less memory to store a long sequence of accesses and still you retain full samplerate time resolution. This is a very powerful feature when dealing with microprocessor circuits like the ones you are describing. Another possibility is to take a snapshot of samples around an event which can help to find what the signals look like before and after an event (for example: see what happens in surrounding logic when a setting in hardware is changed).
The TLA7N4 module can be hacked to support 8Mpts per channel. You have to send a few simple commands over the TekVISA control panel to do this. More info can be found on this forum.
--- End quote ---
Thank you very much for chiming in about the TLA715! There is a lot of great knowledge in this forum about this unit. I am going to check out the one local to me this week. I don't have anything with Mictor connectors that I can test the unit with. Is there any other way I can test the logic analyzing capability of the unit without buying some probes I can test with? Of course I am going to do the obvious inspecting and testing that I can do. Any cons or things you wish it did that it doesn't?
--- Quote from: artag on June 15, 2024, 03:56:02 pm --- They might be useful to sku_u but he's looking for solutions to microprocessor-based instruments with external ram and rom, which often fail because of address decoding or data bit errors. A wide logic analyser is kind of overkill but does actually do a really good job as long as you have a decent probing solution.
For machines with a 40-pin DIP CPU (a lot of them !) I recommend a 40 pin dip clip with the LA probes connected to address, data and control signals - enough to get an instruction trace. Maybe add a few external signals such as chip selects on rom and ram chips. Capture the first few hundred cycles out of reset. This is long enough to do plenty of instruction fetches and, critically, some stack access,
Examine the trace, verifying :
1. What happens at reset ? Typically it should fetch a reset vector, access a ROM and then start executing there. Is it sensible ?
2. Are all the data bits active ? any appear to be shorted together or stuck high / low ?
3. Watch a call occurring (the PC should get pushed onto the stack, maybe with other things)
4. Find the corresponding return. Does the same value get pulled from the stack or has it been corrupted ?
These will show up most of the common problems around a CPU/RAM/ROM core. You might be able to extend it to some I/O and a larger range of address bits but I have used this heavily when training production technicians to debug new builds that pass ATE but don't work. Both 8086 and ARM2/3 machines. These are especially hard because they often have multiple faults - they have NEVER worked. Most repairs are on bits of equipment that worked until they got a fault and then were sent for repair - so they only have one fault. Old equipment thats been rusting for years may have more but they're often in very different areas (logic, power supply, hard discs).
This procedure feeds back into the initial question slightly.
You want an LA that's wide enough for all address, data and control buses and a few extra too. This means 32 bit for 8 bit machines and more for 16 bit machines. Not many 32 bit busses in this era. but Acorn Archimedes is an exception - though the conditional instructions makes it a bugger tom determine execution path other than through the address bus.
Some machines (8086, Z80) have a multiplexed address/data bus. Thius reduces the nuber of pins you need to moinitor but requires a state clocking mechanism that can record both data and address phases. I think this needed an external hardware bus processor for the 8086.
Huge depth is not necessary (though it's nice). Even with 1k depth you'll usually see a stack call & return, and if necessary you can trigger on ram accesses over a small address range. This is the advantage of the complex state triggers these LAs have.
A disassembler (possibly including special hardware) is also very helpful to make the instruction stream more readable.
--- End quote ---
Some fantastic information here!!!
--- Quote from: artag on June 15, 2024, 04:08:06 pm ---Another device that has a bit of a premium price because of rarity and the appreciation of it by, especially, arcade techs, is the Fluke Troubleshooter. This is a simplified in-circuit emulator with personality pods to suit popular processors. The processor is removed and the pod end plugged in its place (it may be possible to clip over a soldered-in device).
The troubleshooter then runs a bunch of canned tests such as ram, rom checksum, address and data bus etc. by generating bus cycles at the processor that exercise those things without requiring the real roms and rams to work. I think it has an actual processor in the pod, it's not just a digital vector generator, but that processor is using its own rom and ram and then steering the bus access internally or externally to suit. This can give very rapid detection of shorted or open data and address busses.
I'm not sure if there are enough machine of this era needing repairs to justify the development effort, but it could be reproduced using something like a Pico. Maybe worthwhile for fixing pinball machines which have large numbers of different designs having a common CPU board.
--- End quote ---
Fluke 9010A? This looks like such a cool and interesting unit!
--- Quote from: TomKatt on June 16, 2024, 10:24:53 pm ---FWIW I was playing around with my DSlogic LA today and noticed that it has a full Z80 decoder available. You might have to play around with triggering options as discussed above, but you can capture and filter addresses, data R/W etc pretty easily. With the large memory ability provided by streaming capture, you could easily analyze the startup process to verify proper operation.
Just figured I’d mention that as it seems like it would be helpful for working on that type of gear. I see that the OP wants a stand-alone device, so prefers a non usb LA…. But if the tool works for the task I don’t see how that applies to the issue? A stand-alone device is basically the logic hardware with a self contained processor running the box, so what difference would it make if the logic hardware and processor were separate devices? Surely there’s no lack of laptops available to make a dedicated usb LA setup? That’s basically what I do - a cheap older tough Thinkbook makes a good addition to my bench. In addition to running my LA, it also connects to my power supplies, scope, and meters for data logging. It’s a tool like everything else.
Edit - looked up the HP 16500.. very impressive. But obviously bench space is not the limiting factor if you’re looking at gear that size lol.
--- End quote ---
Thank you for chiming in about the Z80 decoder.... this definitely makes it an interesting option. I haven't completely written off an USB based analyzer and I do have an older Thinkpad laying around...
tggzzz:
--- Quote from: sku_u on June 17, 2024, 06:48:16 am ---Thank you everyone for replying. There is a lot of invaluable information in here and a lot of points that I would have not considered if it wasn't for your comments.
Some of the key points I've taken away
-LA should be wide enough for all of the address, data, & control lines
-Triggering options
-Capture depth
--- End quote ---
And filtering operations.
With filtering operations you can avoid capturing irrelevant stuff, e.g.
* irrelevant stuff that will be ignored by the ICs because it is between the ICs' clocks. If the IC ignores it, you shouldn't have to look at it!
* stuff unrelated to a particular suspect peripheral or memory range, or I/O or interrupt lineThose may or may not be inherent in a "personality module" for a specific processor. You may still need them for your system's peripherals.
Good to see someone listening to responses and thinking and replying. :) That doesn't always happen :(
nctnico:
--- Quote from: sku_u on June 17, 2024, 06:48:16 am ---
--- Quote from: nctnico on June 15, 2024, 03:53:03 pm ---
--- Quote from: sku_u on June 15, 2024, 08:17:48 am ---A Tektronix TLA715 is available locally and I am considering this unit but I basically know nothing when it comes to the probes and adapters I need. It has two of the TLA7N4 (2GHz timing, 64k) modules installed and comes with several of the P6434 probes. Of course these probes are the ones with the Mictor connector and are of no use to me unless I buy or make a Mictor to 2.54mm adapter. I need help determining which probes would be most suitable for my application and I have allocated several hundred dollars for obtaining these probes. According to the pdf, "Tektronix P6400 P6800 P6900 Logic Analyzer Probes" from https://w140.com/tekwiki/wiki/P6434, it looks like most of the probes are compatible with TTL & CMOS levels. I need some sort of flying lead that can be attached to the pins of chips. I have made a little DIP-14/16 breakout PCB with 2.54mm pin headers that I can attach a probe to as well. The P6417 and P6418 appear to be something I can use but I would like to confirm.
--- End quote ---
I have a TLA715 myself and so far I've been very happy with it (its my 4th logic analyser). A newer model is the TLA7000 series which can use the same modules.
Having a mictor to flying leads adapter is one way to go. I have made something like that a long time ago.
If you want to hunt for flying lead probes, make sure to get the P6417. These are the older model which has tongue shaped contacts which will grab on thin wires as well.
I see some mentioning getting USB logic analysers but I don't think these are very handy as these don't have the elaborate trigger and storage qualifiers a real logic analyser has. What the TLA715 can do is store only when a signal changes. This means A) you can use read/write strobes, chip selects, etc to get a list with addresses a microprocessor is accessing and thus trace which memory locations are accessed B) you need far less memory to store a long sequence of accesses and still you retain full samplerate time resolution. This is a very powerful feature when dealing with microprocessor circuits like the ones you are describing. Another possibility is to take a snapshot of samples around an event which can help to find what the signals look like before and after an event (for example: see what happens in surrounding logic when a setting in hardware is changed).
The TLA7N4 module can be hacked to support 8Mpts per channel. You have to send a few simple commands over the TekVISA control panel to do this. More info can be found on this forum.
--- End quote ---
Thank you very much for chiming in about the TLA715! There is a lot of great knowledge in this forum about this unit. I am going to check out the one local to me this week. I don't have anything with Mictor connectors that I can test the unit with. Is there any other way I can test the logic analyzing capability of the unit without buying some probes I can test with? Of course I am going to do the obvious inspecting and testing that I can do. Any cons or things you wish it did that it doesn't?
--- End quote ---
The acquisition module can run a diagnostic self-test which should tell you whether they work (or not).
The only wish I have is that the software should run a bit faster. I'm using my TLA715 remotely from my PC (using the same software as runs on the logic analyser) which is great because the bigger monitors and mouse + keyboard make life a lot easier. Nevertheless the software remains quite slow; it doesn't load the processor anywhere near 100% so the slowness seems to be on purpose for some reason.
TomKatt:
--- Quote from: sku_u on June 17, 2024, 06:48:16 am ---Thank you for chiming in about the Z80 decoder.... this definitely makes it an interesting option. I haven't completely written off an USB based analyzer and I do have an older Thinkpad laying around...
--- End quote ---
I suspect the Tek TLA715 is in an entirely different class compared to my DSlogic LA lol. Nonetheless, for informational purposes here is what the Z80 decoder menu looks like...
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