topic Re: can only read/write 64 byte to SDRAM in LPC Microcontrollers

can only read/write 64 byte to SDRAM

lpcware — Wed, 15 Jun 2016 17:37:18 GMT

Content originally posted in LPCWare by Alex on Thu Oct 30 05:58:45 MST 2014
Hi,

I did a board design with a LPC1778 and an ISSI IS42S16100E SDRAM.
unfortunately I missed to connect the correct bank address line to the SDRAM. I connected P4.11 of the LPC to A11 of the SDRAM but as it is the bank address I should have connected P4.13 instead.

Currently I don't manage to get any data exchanged with the SDRAM. My question is if this is a result of the wrong bank address or if it is something else.

I would expect that at least one bank is working.

I attached a source file with my initialization code.

EDIT: My test code is able to write 64 byte to SDRAM and read it back. If I try to write more data, nothing is written. Does it only seem to be working due to buffering or is it working but there is a problem with row switching?

Thank you in advance.

kind regards
Alex

Original Attachment has been moved to: board_lowlevel.c.zip

Re: can only read/write 64 byte to SDRAM

lpcware — Wed, 15 Jun 2016 17:37:19 GMT

Content originally posted in LPCWare by dbtayl on Thu Oct 30 08:39:02 MST 2014
It says in the SDRAM datasheet of A11: "This signal becomes part of the OP CODE during mode register set command input."

Maybe that's part of your issue?

Re: can only read/write 64 byte to SDRAM

lpcware — Wed, 15 Jun 2016 17:37:20 GMT

Content originally posted in LPCWare by Alex on Thu Oct 30 08:42:11 MST 2014
The Opcode is used only during the mode set command. I set the IOCON register for P4.11 to 0x28 to make sure that it is used as GPIO. Also is the pulldown enabled to make sure it has the correct level.

Re: can only read/write 64 byte to SDRAM

lpcware — Wed, 15 Jun 2016 17:37:20 GMT

Content originally posted in LPCWare by dbtayl on Sat Nov 01 07:21:42 MST 2014
I should note that I really don't know what I'm talking about- I've never tried to use an external RAM module with a micro before, so I'm just throwing things out based on what I see in the datasheet.

My thoughts (see above if any of them are really dumb):

-You're observing the write-recovery period when trying to write to the RAM?

-The RAM specifies 200/166/143 MHz operation. I assume you're going slower than that. Is that a problem? Or that's just the max frequency, so anything under that is OK (probably the latter, but hey)?

-It looks like the RAS strobe has a higher latency than other timings- is that accounted for? Seems like it might jibe with the "64 bytes" part of your problem.

-Have you tried writing to a DIFFERENT 64-byte area of memory? Does that work OK?

-Can you re-write and re-read the same 64 bytes (eg, write 0x333333..., read it back, write 0x555555.... to the same location, read it back)?

-Are you sending the RAM commends to set the parameters you assume (and/or they match the defaults)? Things like burst length, CAS latency, etc.?

Hope something there helps! If it's not some stupid little mistake, I don't know if I can help any more than that- you'll need somebody that knows what they're doing.