Proper mpc5777m memory address connection

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Proper mpc5777m memory address connection

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nicholaswernick
Contributor I

Electrical Engineer connecting mpc5777m EBI to a RAM chip. I am curious if I have connected the memory address lines correctly.

The mpc5777m EBI is connected to an SRAM BGA with 1024x 16 bit words and 19 address pins. I added a 20th address pin in case I use the 2048x 16 bit word version of that chip.

PowerPC is opposite endian, so I think that means address bit 31 from the processor is connected to address 0 of the RAM. PPC Address bit 12 is RAM bit 19. PPC bit 11 would be RAM address bit 20.

Then there are Byte enables. PPC 'address bit' 9 would be lower byte enable. PPC addr bit 8 would be upper byte enable.

Is my logic correct? Here are images of my wiring:

pastedImage_1.jpg

pastedImage_2.jpg

7 Replies

527 Views
dukaizhu
Contributor I

If  APS=1, then can external address line A31  be connected to A0 pin of external flash or SRAM(16bit data bus)? Is the connection right?

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davidtosenovjan
NXP TechSupport
NXP TechSupport

Hi, please take a look at following document, especially section 3, 4, 6:

https://community.nxp.com/docs/DOC-101725 

I believe it answers your question.

527 Views
jschloss
Contributor III

Does the "address by port size" bit (EBI_OR[APS]) allow the address lines for a 16 bit data port memory to start at 31 instead of 30?

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davidtosenovjan
NXP TechSupport
NXP TechSupport

Theoretically yes, but I know an erratum exists for MPC5777C device:

pastedImage_1.png

If you are in design stage I would rather recommend to connect it usual way.

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jschloss
Contributor III

We decided to try it, looks like APS=1 is working for us on the MPC5777M, so we are able to use the address line that would otherwise be unusable due to byte select muxing.

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dukaizhu
Contributor I

If  APS=1, then can external address line A31  be connected to A0 pin of external flash or SRAM(16bit data bus)? Is the connection right?  what is the result of your trying?

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nicholaswernick
Contributor I

Is there a way to know if this errata also affects the MPC5777M? Does this errata also affect the 77M?

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