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| MMC |
 Posted: Fri Nov 25, 2005 10:52 am |
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Hello,
Can anyone tell me where to get info on using an MMC. A good place to start ( I guess) would be a manufacturer data sheet.
Thanks in adavance |
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JBM
Joined: 12 May 2004
Posts: 54
Location: edinburgh, Scotland
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| Posted: Fri Nov 25, 2005 11:34 am |
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Look in the code library. It makes a good start.
Glad to see you did a thorough search before posting..... |
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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asmallri
Joined: 12 Aug 2004
Posts: 1635
Location: Perth, Australia
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| Posted: Sun Nov 27, 2005 10:13 pm |
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The voltage divider approach works well however there is a problem with the posted solution. The 3.3V SDI input to the (SDO from the MMC) is not good enough. It may work but is outside the specifications for the port. For example, the minimum high voltage of the SDI input on a PIC18F252 is 0.7xVDD = 3.5 volts which is above the 3.3 volts from the MMC card. If you want to use the SPI port to talk to the MMC (and who wouldn't) then you need to use an external buffer with TTL level inputs. Interestingly, if you were to implement a SW SPI interface using PortB on the same PIC then you would not have a problem as these inputs are TTL inputs with a minimum input high voltage of 2.0V with +5V VDD.
_________________
Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!
Last edited by asmallri on Mon Nov 28, 2005 8:49 am; edited 1 time in total |
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Matze
Joined: 28 Nov 2005
Posts: 2
Location: Saarland, Germany
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| Posted: Mon Nov 28, 2005 8:01 am |
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Hello,
on http://www.ulrichradig.de -->"avr - projekte" --> "MMC - SD" is a good explanation for mmc/sd carts and µC |
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asmallri
Joined: 12 Aug 2004
Posts: 1635
Location: Perth, Australia
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| Posted: Mon Nov 28, 2005 8:58 am |
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| Matze wrote: | Hello,
on http://www.ulrichradig.de -->"avr - projekte" --> "MMC - SD" is a good explanation for mmc/sd carts and µC |
It helps if you can read German :-)
The "premium" interface is a bit of an overkill with 20 components plus the power supply but I have no doubt it will do the job however the minimal implementation has the same problem (if used with a PIC's SPI port) as mentioned previously.
_________________
Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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Matze
Joined: 28 Nov 2005
Posts: 2
Location: Saarland, Germany
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| Open-drain level translators for the MMC card |
| Posted: Tue Dec 13, 2005 4:16 pm |
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My question is somewhat related to the original one. I’m designing hardware for the MMC card for the first time. PIC and most of my system is powered by +5V, and the MMC has its own +3.3V regulator. Of course there need to be logic level translators between the MMC and PIC. I have found some level translators, which are 5V-tolerant and have open-drain outputs. SN74LVC3G07 My plan is to use 2 of these chips, power both of them with +3.3V and pull the outputs to their respective output voltages: SDI to +5V, SDO, CS#, SCK to +3.3V
My questions are:
- Do you think these level translators will work?
- How can I estimate the maximum bit rate?
- What level translators have worked well for you in the past?
Thanks! |
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