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PIC port expansion

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2005-2006 » Archive through 11 June, 2006 » PIC port expansion « Previous Next »

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Eagre
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Post Number: 65
Registered: 05-2005


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Posted on Tuesday, 30 May, 2006 - 01:08 am:   Edit Post Delete Post Print Post

In seem to recall an EPE article concerning expansion of the number of PIC outputs using serial-to-parallel ICs, I think it is a great idea. I can't locate the reference, and my site searches have found nothing. I assume it involves 74xx164s or 74xx595s. Any info ?

Ed Grens
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John_becker
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Post Number: 355
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Posted on Tuesday, 30 May, 2006 - 01:32 am:   Edit Post Delete Post Print Post

I think there was Ed but I dont have records here to check. I wonder if Mike Hibbett or anyone else might recall ?

J
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Not_a_number
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Post Number: 21
Registered: 08-2005

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Posted on Tuesday, 30 May, 2006 - 02:04 am:   Edit Post Delete Post Print Post

Hello Ed,

Are you aware that Microchip manufacture several dedicated I/O expanders, MCP23008 etc?


- NaN
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Scott2734
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Post Number: 78
Registered: 10-2005

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Posted on Tuesday, 30 May, 2006 - 03:33 am:   Edit Post Delete Post Print Post

The maxim 7311 can do that.
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3727
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Mikehibbett
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Post Number: 450
Registered: 04-2005

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Posted on Tuesday, 30 May, 2006 - 03:49 pm:   Edit Post Delete Post Print Post

PIC I/O expansion is the topic of a PicNMix article - recent one, might even be this months.

There are several techniques, depending on exactly what you want to do.

Mike.
-----
www.drivesentinel.co.uk - Home build GPS Speed Camera Detectors
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Eagre
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Post Number: 66
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Posted on Wednesday, 31 May, 2006 - 04:26 am:   Edit Post Delete Post Print Post

Thanks all for your responses. There appears to be no PIC n MIX article on this in 2006, although I seem to remember such an article. The website search engine is not very helpful.

I would prefer an expansion using a 74HCT164 (USD 0.30) to a more expensive solution. This implementation would appear to take just two PIC outputs (clock and data, the other data line tied high).

Ed Grens
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Scott2734
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Post Number: 79
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Posted on Wednesday, 31 May, 2006 - 04:48 am:   Edit Post Delete Post Print Post

If you go to the maxim website, you can get free samples of these chips.I cant remember the series of the dip ones tho, you will have to look through them. The series start at 7300 and go to 7318 i think.
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Dave_squibb
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Post Number: 54
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Posted on Wednesday, 31 May, 2006 - 09:55 am:   Edit Post Delete Post Print Post

This is covered in "Circuit Surgery" on page 27 of the April 06 issue.
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John_becker
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Post Number: 361
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Posted on Wednesday, 31 May, 2006 - 11:33 am:   Edit Post Delete Post Print Post

What I'm thinking of far pre-dates PnM or current CS. From some years ago it would have been, but I just dont recall details.

J
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Pwillard
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Post Number: 31
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Posted on Wednesday, 31 May, 2006 - 06:44 pm:   Edit Post Delete Post Print Post

There is also the 2-wire I2C based method using PCF8574 8 bit bidirectional I/O device. It's an older, cheaper device but there a lot articles on the web on how to go about using it.

Mike Predko also explains in his books how to use the 74LS174 (http://www.myke.com/graphics/2wirelcd.jpg) in a 2-wire mode for driving LCD's.
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741
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Post Number: 31
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Posted on Wednesday, 31 May, 2006 - 08:29 pm:   Edit Post Delete Post Print Post

If 4-> 8,16,24... is what you need then:
Try a CD4094 "8 stage shift and store bus register".
You simply use the STROBE pin to disable the output.
Now you clock the pin data in using DATA and CLOCK pins, then enable.
The DS shows that you can cascade the chips.
(4094 is cheap as chips)

(Message edited by 741 on 31 May, 2006)
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Atferrari
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Post Number: 191
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Posted on Friday, 02 June, 2006 - 12:31 am:   Edit Post Delete Post Print Post

741,

I agree.
Found the CD4094 one of the simplest to use, quite effective and always working well with Vdd 5V.
Agustín Tomás - Buenos Aires - Argentina
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Not_a_number
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Post Number: 22
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Posted on Friday, 02 June, 2006 - 01:23 am:   Edit Post Delete Post Print Post

I'm not sure on this, but isn't the maximum current that a CD4094 can source or sink quite small relative to a standard PIC output or a dedicated I/O expander?

- NaN
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Atferrari
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Post Number: 192
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Posted on Friday, 02 June, 2006 - 08:26 am:   Edit Post Delete Post Print Post

Yes, your are right. It follows the CD4XXX specs.
Agustín Tomás - Buenos Aires - Argentina
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John_becker
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Post Number: 363
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Posted on Friday, 02 June, 2006 - 09:26 am:   Edit Post Delete Post Print Post

But many of the devices are repeated in the 74HC series which can deliver/sink higher currents, 20/25mA I think. Normal 4000 series is about 4mA if you're lucky.

J
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Zeitghost
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Post Number: 200
Registered: 01-2006

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Posted on Saturday, 03 June, 2006 - 05:08 pm:   Edit Post Delete Post Print Post

I worked on a telephone product that used shift registers for I/O expansion.

It was truly hideous.

Though it did work.

Sort of.
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Not_a_number
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Post Number: 23
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Posted on Wednesday, 07 June, 2006 - 08:32 pm:   Edit Post Delete Post Print Post

Hello John,

Does the CD4094 approach also convey the added benefit of arbitrary data direction?

- NaN
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John_becker
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Posted on Thursday, 08 June, 2006 - 12:28 am:   Edit Post Delete Post Print Post

4094 is not a device number I'm familiar with NaN, sorry. Check the datasheet.

J
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Atferrari
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Post Number: 194
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Posted on Thursday, 08 June, 2006 - 01:23 am:   Edit Post Delete Post Print Post

No, data input is in one direction, always.

The best is the strobe. Once activated all data appears at the outputs at once.

Series to parallel converter. Understanding it from the datasheet is simple.
Agustín Tomás - Buenos Aires - Argentina
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Eagre
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Post Number: 68
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Posted on Friday, 09 June, 2006 - 01:07 am:   Edit Post Delete Post Print Post

Again, thanks all. Dave's reference to the Circuit Surgery article was what I was looking for. The 74HC595 will handle +-6mA loads. Unfortunately, I cannot find a source for a 74AC(or ACT)595, which would handle +-24mA loads. The version with OC output does not meet my needs as I must source, as well as sink, current.

Ed Grens

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