regarding external memory access in NE64 controller

[rammohank]

hi frnds,

i am using NE64 controller in my project. we are planned to use normal expanded narrow mode as we have one external 8 bit NVRAM. i like to know how to interface the NVRAM chip to the controller. and also how to demultiplex the address and data lines.

Is XCS signal is reqd for demultiplexing the address and data bus??

regards
rammohan

[Ilocano]

Below app note may shed some light for your question.
http://www.freescale.com/files/microcontrollers/doc/app_note/AN2287.pdf
http://www.freescale.com/files/microcontrollers/doc/app_note/AN2408.pdf

Note that if you stick external mem to NE64, the bus speed or ECLK is max 16MHz as per specs. This is only good for 10BaseT

[nerdboy]

Thanks for the info. I have a tricky question along the same lines.

You say (as does the documentation) that the max external bus speed is 16MHz, which limits you to 10BaseT. On the evaluation board, they are clocking the external memory at 25MHz - with a provided note that this should only be used in a lab environment. So it must be possible to achieve 25MHz bus speed. In the device datasheet (page 537) under the frequency range for the bus clock with external memory and 100BaseT they say "Not available". Does this mean "Not recommended" or is there something in place that physically prevents you from doing this?

I'm really quite disappointed that this chip supposedly can't do 100BaseT with an external memory interface. I wrote some code in which I manually access the external memory, and looking at the disassembled code, it is at least ten times less efficient.

Does anyone have an answer to my question in the first paragraph? Any other suggestions? I want to use the NE64 to send UDP packets produced by an FPGA (I'm interfacing with the FPGA memory).

Thanks!

Jeff

[imajeff]

Yes it must be possible to achieve 25MHz bus speed. That is internal (single chip mode). But are we not talking about "external bus speed" instead? That's not possible, as everyone agrees.

So the answer is do 100BaseT only in single chip mode. Apparently it works. For this reason, people don't typically design a system with external bus because the MCU would not be able to speed up to 100BaseT.

* edited last line to say external bus (didn't mean internal)

Message Edited by imajeff on 2006-07-12 03:54 PM

[nerdboy]

Thanks imajeff, but we haven't answered my question. I know that on this forum everyone has agreed that the max external bus speed is 16MHz. However, if you look at the EVB9S12NE64 Manual, Page 10, you will see:

"EVB board operation allows 25MHz external bus operation at 0 clock stretch cycles for development purposes. User should note that the NE64 device has a 16MHz rated external bus capability and that 25MHz operation should not be expected in NE64 product designs."

Again, my question: is there anything physically preventing me from at least attempting to run 100BaseT with the external bus at 25MHz with 0 clock stretch???

Thanks in advance,

Jeff

[imajeff]

Thanks for clarifying what document is in question. Reading back on the thread, I don't see a question regarding the statement specific to EVB9S12NE64, and I would have never read that doc because I do not have the EVB9S12NE64.

I don't mean any malice here, just hope to make it clear enough... So I will help translate the quote you pasted from the doc:

In english, the quote states that the EVB board was designed to run "25MHz external bus operation at 0 clock stretch cycles", and that this will likely do you no good because of the NE64 limitation which we have all agreed upon. Here is a translation of the quote in context of your question, "Hey it's not our fault that you can't run external bus at 25MHz with 0 clock stretch cycles--it's the NE64's fault".

So yes the question has been answered in many ways, including the answer within the quote you posted.

P.S. I guess I should add my opinion that it won't hurt any hardware to try it anyway. They don't say that it will not damage the NE64 but I would guess that it will just not function correctly.

Message Edited by imajeff on 2006-07-14 08:11 AM