Polling SDI whilst using the build in SPI

Torello · Joined: 29 Sep 2006 Posts: 120

Hello,

I am writing code for a serial flash memory (MX25L25635E, 256Mbit). This chip can put the "write in progress" bit out on the SDI line in its several write modes. Polling this bit is must faster then issuing a SPI command to read the status register to get this bit.

Does anybody know if, and how the SDI can be polled whilst the SPI module is enabled?

Regards,
Edwin

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

You would have to disable the SPI module to poll the port
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Regards, Andrew

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Ttelmah · Joined: 11 Mar 2010 Posts: 19529

I don't think you do.
Provided you just read the pin, it should still work. If you look at the port block diagram for a typical chip, the peripheral select turns off the output functions on the port, but the input functions are still left enabled.
_However_, there is a significant caveat. On many chips the SPI input uses a Schmitt trigger input latch, while reading the port uses a TTL latch, so the logic levels you'd be testing would differ from what SPI uses. Might cause a problem...

Best Wishes

Torello · Joined: 29 Sep 2006 Posts: 120

Thanks all,

I think I give it a try. Levels should not be a big issue a I see the signal on the scoop nicely go to 3v as on which flash and pic works.
Problem with the MX25 is that they specify tBP as 9 upto 300us. Well that's quite a range! Surely don't want to wait 300us for each byte.
But also Tpage_program goes from 1.5 to ~5 ms.
And I can't affort flash errors...

Regards, Edwin.
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FvM · Joined: 27 Aug 2008 Posts: 2337 Location: Germany

You should mention the involved processor type. At least for PIC18 and PIC24, the peripheral function doesn't disable the digital input buffer, this is only the case for analog inputs. So a pin read, e.g. by input_state(), is supposed to work on the SDI pin.

Torello · Joined: 29 Sep 2006 Posts: 120

It's a Pic18. I'll give it a try and will report my findings.
Thanks all,
_________________
Regards, Edwin. PCWHD v5.114

Torello · Joined: 29 Sep 2006 Posts: 120

Confirmed! It does work. No need to disable the hardware SPI, you can poll the DI line any time.

regards,
_________________
Regards, Edwin. PCWHD v5.114