nwait pin of emc

[zhonghuiwang]

EMC of all lpc arm has no nwait pin, why?

[Hui_Ma]

Hi

Please let us know which memory/device(part number) you want to use with LPC MCU.

Thank you for the attention.

Have a great day,
Ma Hui
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[zhonghuiwang]

Hi

Thanks for the reply.

I use LPC1788 connect with a ASIC by external EMC bus, the ASIC is a low speed device which has a nwait pin, but LPC1788 has no.

So I adjust the emc bus wait time of LPC1788 to match the ASIC bus timing. I use the maximum read an write time of the ASIC, it can work. But it is unreliable,sometime data is bad.

I carefully read the ASIC’s datasheet, and find this notes: “ To ensure access,XWAIT should be connected to WAIT input of CPU”

So I want to find LPC series( cortex m3 or m4) which has nwait input of EMC bus.

The attachment jpg file is about the timing of ASIC.

Look forward to your reply, thank you!

wang

发件人: bounces+210748-bff3-jijin_fa=163.com@jiveon.jivesoftware.com 代表 Hui_Ma

发送时间: 2017年3月8日 15:31

收件人: zhonghui wang

主题: Re: - Re: nwait pin of emc

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Re: nwait pin of emc

reply from Hui_Ma <https://community.nxp.com/people/Hui_Ma?et=watches.email.thread> in LPC - View <https://community.nxp.com/message/884768?commentID=884768&et=watches.email.thread#comment-884768> the full discussion

[Hui_Ma]

Hi

I checked your attached ASIC Access timing picture.

I am not quite understand the XWAIT signal's function, for the Toe (Output enable time) could make sure the data was ready.

For there with the Max. value of Twaer and Twaphr interval, could you double check with ASIC vendor if there with Max. 225ns delay of Toe signal, if there still need XWAIT be connected ot WAIT input of ASIC?

LPC EMC module could set the Toe delay with Static Memory Output Enable Delay registers[WAITOEN] and  Static Memory Read Delay registers [WAITRD] setting.

Wish it helps.

Have a great day,
Ma Hui
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[zhonghuiwang]

Hi

Thanks for the reply.

The nwait singal is used to prolong a bus cycle. As long as nwait is low, the bus cycle cannot be completed and waits until nwait is high.

So nwait has priority over the Toe delay and read delay. The access timing of some devices is not accuracy(in the datasheet) ,but nwait is accuracy .

Using of nwait is more reliable than time delay in some devices.

I find the arm chip of TI,ST,SUMSUNG has the nwait input, I don’t know why LPC series has no.

I am familiar with LPC MCU, I don’t want to change to others. Do you know which LPC series has nwait input?

Look forward to your reply, thank you!

wang

发件人: bounces+210748-bff3-jijin_fa=163.com@jiveon.jivesoftware.com 代表 Hui_Ma

发送时间: 2017年3月10日 14:50

收件人: zhonghui wang

主题: Re: - Re: nwait pin of emc

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Re: nwait pin of emc

reply from Hui_Ma <https://community.nxp.com/people/Hui_Ma?et=watches.email.thread> in LPC - View <https://community.nxp.com/message/885524?commentID=885524&et=watches.email.thread#comment-885524> the full discussion

[Hui_Ma]

Hi

So far, the LPC EMC module doesn't provide external input pin for external transfer acknowledge.

While, LPC EMC module could set the programmable delay to configure the EMC timing.

And as you know, the new NXP company has another ARM Cortex-M core MCU named Kinetis, which has Flexbus module with /FB_TA pin. That pin is external transfer acknowledge function pin, which could used to control the transfer by external ASIC device.

More detailed info about Kinetis Flexbus module, please check Kinetis related reference manual.

Wish it helps.

Have a great day,
Ma Hui
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