Storing bits using schmitt trigger inverters

OBones · 2005-09-29T03:32:38+00:00

Hi allI've got two lines: 1 data, and 1 clockWhen the clock goes down to up, the data is ok. What I want to do is to have a logic 1 when the data line was 1 for the last two clock "low to high" transitions. If the last two states were not 1, then the output must be a logic 0.At first I though of using two D-Type flip flops (74AC74) in cascade configuration with the Q output of the first one being the input of the second one. Then I "AND" the two Q's and I get the logic 1 I'm looking for. __ .------------| \ .--o--. | .--o--. |08 )- Dta -----|D S Q|--+--|D S Q|---|__/ -|> | -|> | Clk ---+-|C R Q| .-|C R Q| | '--o--' | '--o--' '-----------'(created by AACircuit v1.28.5 beta 02/06/05 However, the room I have on the board is very scarce and I would like to take advantage of the 4 schmitt trigger inverters I have in a 74AC14 chip. This chip is used along with 3 out of 4 AND gates in a 74AC08 to create the above mentionned data line.So here is what I have left:1 AND and 4 Schmitt NOT.Is there a way to create a "1 bit memory" using schmitt trigger inverters? The schmitt trigger inverters could be replaced by regular inverters if need be. They are used to generate the Data line like this: |\ __ Q1 o---|S>O------| \ |/ |08 )---. |\ .---|__/ | __ Q2 o---|S>O--' '--| \ |/ |08 )- Dta __ .--|__/ Q3 o-------------| \ | |08 )---' Q4 o-------------|__/(created by AACircuit v1.28.5 beta 02/06/05 I hope I'm clear enough in my explanations, please do not hesitate to ask questions if need be.Thanks a lot for any help.CheersOlivier

Sep 29, 2005 26 Replies

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Ken Smith 20 years ago

Both the Altera and Xilinx stuff can be downloaded for free. The CPLD can be a ISP type and you can make your own cable.

The Altera CPLDs can be programmed with a totally dumb cable hanging off the parallel port of a PC. You just have to put some series resistors in the cable. The JAM-ISP software can be downloaded for free.

The ICT parts from Anachip can be developed with a free program too but for them you need a programmer since they are not ISP. ICT's place program is the way to go if you are doing a 22V10 design.

-- kensmith@rahul.net forging knowledge

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OBones 20 years ago

Thanks for the details. In the end, I replaced the two inverters by two pairs of JFETs which gave me back the space to put the D-Type flip flops. I know, I know, why did I ask then? Well, curiosity is the main reason.

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Rich Grise 20 years ago

Of course you do - especially with a spec this loose.

Take two pennies out of your pocket and set them on the table in front of you. Call the head '1', and the tail '0'. Voila! Two bit memory! Of course, if you did it with quarters, it'd be a two-bit two bit memory, with apologies to Mr. Woodgate. ;-)

Cheers! Rich

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Joerg 20 years ago

Hello Oliver,

Ah, but where is the sportsmanship? I mean, wouldn't it feel great if you could make a 2bit memory for next to nothing?

Regards, Joerg

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OBones 20 years ago

It sure would, but I don't have the necessary knowledge to create that.

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keith 20 years ago

You can do it for a dime? CoolRunners are in the $1-$2 range, in onesies.

Keith

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John Woodgate 20 years ago

I read in sci.electronics.design that Rich Grise wrote (in ) about 'Storing bits using schmitt trigger inverters', on Sat, 1 Oct 2005:

I thought of it, but managed to resist the temptation.

Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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