Post by thread:[PICLIST] Microchip C Compiler and SPI

I'm trying to figure out SPI operation in the Microchip C Compiler. As I understand it, writing outgoing data to SSPBUF causes that data to be loaded into SSPSR, which then shifts it out. As data is being shifted out, input data is being shifted in to SSPSR. On completion of the shift in and out, the received data in SSPSR is put in SSPBUF so it can be read. So far so good. Looking at the C compiler library documentation on the SPI library, it LOOKS like BOTH WriteSPI and ReadSPI initiate an SPI bus cycle. It seems to me that only WriteSPI should do that. ReadSPI would then pick up the data received during the previous write. How does this actually work? Actually, I could imagine a function called SPIrw that would have a prototype of unsigned char SPIrw (unsigned char DataToSend) You'd pass it the data to send and it would return the received data. But, that doesn't seem to be how it works. So, how DOES it work? Thanks! Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Still trying to figure out the Microchip C compiler libraries for SPI. I'm successfully sending stuff to shift registers and reading stuff from shift registers. Next job is a full SPI with simultaneous shift out and in. Anyone used Microchip libraries for this? The problem is that it APPEARS (according to the documentation) that BOTH WriteSPI and ReadSPI initiate an SPI bus cycle. So, if I write something out, then read, it seems as though the read is from a second bus cycle (which sent something out to the SPI device also). So, should I just do writes, then read the input from the SSPBUF after DataRdySPI goes true? Anyone doing SPI with these libraries? THANKS! Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

>The problem is that it APPEARS (according to the documentation) >that BOTH WriteSPI and ReadSPI initiate an SPI bus cycle. I have not used SPI, but if I remember correctly from my perusal of the documentation, to read a character from the SPI, it does a dummy write. The SPI hardware then thinks it is writing a byte out to the bus, and so generates clocks which are actually reading in a byte. The apparent write is needed for the clock generation to occur. I have done this trick on other hardware I was involved with for this exact reason, it was the only way to make the clock generation circuit work correctly. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Hi, an SPI *read* is performed by a dummy *write* ( normally sending 0x00 ). It doesn't really matter as you have dedicated lines for DIN and DOUT. However if using s/w spi make sure that the DOUT line does not contain any 'valid' data when reading, normally all 0's is ok. /Tony -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Since I was concerned about the read doing another SPI cycle, I just went right to the register using code like this: WriteSPI(ToExtSpi2.byte); // Send the next byte while(!DataRdySPI()); // Loop until data ready FromSpi2.byte=SSPBUF; // Read the next byte Seems to work. I've got it talking to a Maxim MAX3100. Thanks for the help! Harold On Fri, 17 May 2002 08:23:52 +0100 "Alan B. Pearce" <.....A.B.PearceKILLspam@spam@RL.AC.UK> writes: {Quote hidden}> >The problem is that it APPEARS (according to the documentation) > >that BOTH WriteSPI and ReadSPI initiate an SPI bus cycle. > > I have not used SPI, but if I remember correctly from my perusal of > the > documentation, to read a character from the SPI, it does a dummy > write. The > SPI hardware then thinks it is writing a byte out to the bus, and so > generates clocks which are actually reading in a byte. The apparent > write is > needed for the clock generation to occur. > > I have done this trick on other hardware I was involved with for > this exact > reason, it was the only way to make the clock generation circuit > work > correctly. > > -- > http://www.piclist.com hint: PICList Posts must start with ONE > topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: > ->Ads > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body