timing problems with port

[juergen239955]

Posted on September 14, 2004 at 12:27

timing problems with port

[juergen239955]

Posted on September 02, 2004 at 05:07

Hi,

I have following problem: I use the ST10F269 and I want to send and receive data via the SSC to a flash. For this I use for example following function: int readStatusRegister(unsigned int chipSelect) { int data; // part 1: set chip select P2 &= ~chipSelect; SSCTIR = 0; SSCRIR = 0; // part 2: send RDSR to the flash SSCTB = FLASH_RDSR; while (!SSCTIR) ServeWatchdog(); SSCTIR = 0; // part 3: generate clock to read data from flash SSCTB = FLASH_RDSR; while (!SSCTIR) ServeWatchdog(); SSCTIR = 0; // part 4: get readed data from SCC while (!SSCRIR) ServeWatchdog(); data = SSCRB; SSCRIR = 0; // part 5: reset chip select P2 |= chipSelect; return data; } If I do it in this way, the chip select is resetted (part 5) while I generate the clock (part 3). But the chip select should be resetted after I readed the data (part 4). Do you have any idea, what I have to do to get this? Regards, Juergen

[juergen239955]

Posted on September 02, 2004 at 10:54

I use the M25P10 of ST.

But my problem has nothing to do with this flash. My problem is, that the chip select which I realized over P2 is resettet BEFORE I read the data out of the SCC. What I need is that the chip select is resettet AFTER I read the data out of the SCC.

[tom7]

Posted on September 13, 2004 at 14:55

Juergen,

you may have run into the following problem, caused by the buffered SSCTB... int readStatusRegister(unsigned int chipSelect) { int data; // part 1: set chip select P2 &= ~chipSelect; SSCTIR = 0; SSCRIR = 0; // part 2: send RDSR to the flash SSCTB = FLASH_RDSR; while (!SSCTIR) ServeWatchdog(); SSCTIR = 0; *** here your data was placed inside the SSC-Tx, now SSCTIR is set and data gets physically clocked out... // part 3: generate clock to read data from flash *** you write the SSCTB (Tx of your first data might be ongoing by the SSC hardware...) SSCTB = FLASH_RDSR; while (!SSCTIR) ServeWatchdog(); *** Tx of first data is now finished - so does reception, *** SSCRIR gets set ! *** SSCTB content gets shifted to SSC-Tx HW reg. and... *** from here Tx starts physically, SSCTIR gets set by HW ***and you are immediately here, even if your second data hasn't been completely sent *** SSCRIR is already set from first data transmission... // part 4: get readed data from SCC while (!SSCRIR) ServeWatchdog(); data = SSCRB; SSCRIR = 0; *** so you fall all the way through, even if your second data is still transmitting... // part 5: reset chip select P2 |= chipSelect; return data; } Do you have any idea, what I have to do to get this? *** yes, in polling mode always use SSCRIR to detect the finished sending of a data item on the SSC, reset SSCRIR, send second data... Regards, ** have fun Juergen ***tomas

[juergen239955]

Posted on September 14, 2004 at 06:07

Hello Tomas,

thank you very much, but I don't think, that this happens. I need the first sended byte to tell the M25P10 that I want to read out the status register. The second byte is sended only to generate the clock which I need to read out the data serially. So the SSCRIR should be set after the second byte is sended and the whole byte is read in. I attache a hardcopy of my oscilloscope to show what happens. channel 1: chip select channel 2: sended data channel 3: received data channel 4: clock Here you can see that the chip select is resettet, while the second byte is sended. Or am I wrong? ________________ Attachments : TEK00000.PCX : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006I0K4&d=%2Fa%2F0X0000000bXU%2FTASDONIrAld.F1I037vBjXvNG4A4nakuDtr_bxExqVc&asPdf=false

[tom7]

Posted on September 14, 2004 at 12:27

Juergen,

Sending implies receiving with the ssc device, so SSCRIR gets set when you send your first data byte and you are polling exactly this. try this : -switch CS active -send first byte -poll SSCRIR until it's set - reset SSCRIR - send second byte -poll SSCRIR until it's set - reset SSCRIR switch CS off that will certainly work , tom.