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silly digital specs on analog parts

This is from the LTC1660 data sheet:

CLR (Pin 11): Asynchronous Clear Input. All internal shift and DAC registers are cleared to zero at the falling edge of the CLR signal, forcing the analog outputs to zero scale. CMOS and TTL compatible.

So, why does an async input act "at the falling edge"?

This is typical for the digital spec sections of ADC and DAC data sheets. It's unclear whether things are level or edge sensitive, active high or low, and often what things actually do.

Same sort of thing for the strobe input on LTC1596. It's not absolutely clear if this is level or edge sensitive.

All the mixed-signal people seem to do this sort of thing.

John

Reply to
John Larkin
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"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

I can check, I use the 1665 (8bit version) with the 1660 as a drop in alternate.

Cheers

Reply to
Martin Riddle

I'm pretty sure it's a static clear. It's just that most mixed-signal parts have bizarre digital interfaces, poorly defined.

John

Reply to
John Larkin

Mixed-signal sims seem to be similar. Trying to learn Orcad-PSpice. Sez GND node is floating but it _is_ connected. Sez "warnings have been generated" and the whole session log just went AWOL. Output flatlines. Hurumph. I am not having fun.

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Regards, Joerg

http://www.analogconsultants.com/

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Reply to
Joerg

Joerg, Take a look at my website at

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You will find that only the 0 (zero) ground works in PSpice. Any other ground is verbotten. Just clidk on the ground symbol and rename it to 0 is the fastest way to solve...

Charlie

Reply to
Charlie E.

"GND" requires a node that is labeled 0 (zero)... no zero node, barf, because a reference point is needed.

PSpice mixed signal is the easiest simulator in the world to learn (which is why Cadence is trying to kill it).

What are you having trouble with?

I've found that any error message results because I did something dumb... usually floating nodes.

One trick I've learned is to go in and edit parts where pins don't actually need a connection, like outputs, and change "error on float" to "don't care" ;-)

(I keep my own symbol library, and haven't let OrCAD "update" my libraries for years. MyLMC555 that I just posted uses a "canned" symbol for the graphic, but is otherwise "attributed" to suit ME :-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed
Reply to
Jim Thompson

Or go into the symbol libraries and permanently change all ground symbols to be "LABEL=0" ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed
Reply to
Jim Thompson

BTW, Joerg, That error is so common for a new user that I tried for YEARS to get them to change the error message to add "Did you use 0(source) as your ground?" but since everyone hits that problem once, but usually not too many times later, they thought it unnecessary... :-(

The more fun version of this is when you use the wrong grounds, but have an opamp or other model that has 0 used internally. This causes the entire simulation to use that internal ground as the ground reference point, so you see all kind of wild voltages around the circuit, especially on the 'ground' node!

Charlie

Reply to
Charlie E.

But they are still selling it. Not sure about the easy learning part. LTSpice took me just a couple hours, and that was coming from a pure netlist or text entry mode that I was used to. With this Orcad I am well beyond 2h. The schematic part is also not like it was in the good old times. SDT was better, and so is Eagle, IMHO.

I'll have to figure this out but don't want to spend too much time developing a repository if possible. I mean, it just warned me that it can't find any templates. Not even for a lowly LM324.

Thanks, Charlie. Found out the ground thing the hard way, by trial and error. A wee warning blurb from the software woulda been nice ...

Yeah, LTSpice somehow doesn't do that stuff. It always works. I am seeing engineers move to that in droves, easy learning and it's free. Another project I am consulting for right now is a chip design and when I showed LTSpice to the IC designer at my client he was mighty impressed.

I have to use Orcad this time, client preference.

Oh well, it's really cold outside and pouring rain, good CAD learning weather :-)

--
Regards, Joerg

http://www.analogconsultants.com/

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Reply to
Joerg

I don't see the issue. Acting at the falling edge would imply that holding it at zero for some period afterwards won't prevent the DAC from functioning. This might not be true, of course, but that would simply mean it was incorrectly specified.

If the analogue signal were passing through the device, rather than being generated by it, then one would have to wonder what an edge triggered clear meant, but that's not the situation described.

Sylvia.

Reply to
Sylvia Else

Are you trying to use Capture (gag me with a spoon :-)?

PSpice Schematics makes even LTspice look difficult.

It's certainly there in PSpice Schematics but, as usual, I rolled my own... most "public" models are crap.

You can use PSpice Schematics and then roll them into OrCAD by pushing a button. That's how I handle clients that want OrCAD Crapture output. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed
Reply to
Jim Thompson

It appears to be a static clear, level-sensitive and not edge-sensitive.

Instead of "at the falling edge" they should have said "held clear when the pin is low" or some such.

My point is that many, or most, mixed-signal parts have fuzzy digital specs. Some of the serial dac timing diagrams are ghastly. Most, actually.

An opamp with a "clear" input?

John

Reply to
John Larkin

Third error... the key word is Crapture... that's not a problem in PSpice Schematics. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed
Reply to
Jim Thompson

[snip]

Forgot to add... as an "advanced user" I do have a node-to-node part, but it's only really necessary so I can keep names straight when I strip off the test elements from the cell/subcircuit/whatever I am developing. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed
Reply to
Jim Thompson

Yup. It came together with it.

[...]

I'll have to do sims based on existing Orcad schematics, so no choice. Haven't used that CAD in a long time and after trying the newest version a little I must say that I've seen better. It just flagged "Less than 2 connections at node N17378162" where that clearly is baloney (you can move all three parts that are connected and the wires move along with them).

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Regards, Joerg

http://www.analogconsultants.com/

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Reply to
Joerg

Have fun ;-) And enjoy the rain and the cold. We're in the low 80's here. Though they're saying Tuesday will drop down to 73°F :-( ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed
Reply to
Jim Thompson
[...]

We are shoving one load after the other through the wood stove :-(

--
Regards, Joerg

http://www.analogconsultants.com/

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Reply to
Joerg

Because it is a press and release button.

Reply to
TheQuickBrownFox

Joerg, If you need any help, feel free to give me a call. I used to be pretty good at this stuff... ;-)

Charlie

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Reply to
Charlie E.

You really should have had a look at my website. I don't call it the newbies guide to PSpice for nothin'! I took the top few questions we always got on the support line, and gave the answers!

Charlie

Reply to
Charlie E.

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