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spamiam
Joined: 13 Nov 2005
Posts: 665
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Posted: 31 October 2006, 23:29 PM Post subject: Follow-up on H/W SPI interface to MMC card |
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I finally got out my order for some 74HCT08 quad AND gates.
I replaced the 4081 type of AND gate, and the interface stopped working!!!
It would not work even at the slowest speeds. I was thinking that noise in my system was making it fail. I thought that the breadboard was a bad combo with high speed logic.
Well, I went back to the basics... I looked at the spec sheets. Turns out that the pin outs are different!
Once I fixed that up, it worked. It would work all the way up to CLK/2. That means that the bit rate is 7.5 Mhz. Not too shabby.
I will post the final circuit diagram.
-Tony |
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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 31 October 2006, 23:37 PM Post subject: Re: Follow-up on H/W SPI interface to MMC card |
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| spamiam wrote: | | Turns out that the pin outs are different! |
Yep! The 4000 series CMOS is not pin compatible with with the 74xxx series. That's one of the reasons for the greater popularity of the 74HC series compared to 4000 series. |
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spamiam
Joined: 13 Nov 2005
Posts: 665
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Posted: 01 November 2006, 0:18 AM Post subject: Re: Follow-up on H/W SPI interface to MMC card |
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| dkinzer wrote: | | Yep! The 4000 series CMOS is not pin compatible with with the 74xxx series. That's one of the reasons for the greater popularity of the 74HC series compared to 4000 series. |
Well, it caught me with my pants down. I had assumed that the pins would be the same, especially because the 4081 has such a symmetrical ordering of inputs and outputs. The symmetry is go beautiful, I could not imagine anyone breaking the symmetry!
Live and learn.
-Tony |
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