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You can use the PLL Clock Out Divide bits (PLLCOD[1:0] - Bits 11-10) in the
PLL Divide-By Register (PLLDB), to divide the PLL output by 1, 2, 4, or 8, so you can get IPBus clock frequencies of 40, 20, 10, or 5 MHz. Please see Section 15.6.2 "PLL Divide-By Register (PLLDB)", and Section 15.6.2.3 "PLL Clock Out Divide (PLLCOD[1:0] - Bits 11-10)", in the DSP56F80x User's Manual. The 5 MHz IPBus clock would give you a lowest CANbus frequency of: ( 5MHz / ( 24 * 64 ) ) = 3255.2 Hz (approximately) The only drawback to the above, is the reduced operating frequency of the whole chip. Using the EXTAL clock (which is another possibility for the CANbus clock source) is NOT recommended, as there have been several reports of CANbus system failures when using EXTAL as the CANbus clock source. Please also see the following message I posted to this discussion group: October 1, 2002, at about 8:01am: "RE: [motoroladsp] MSCAN problem" The following Application Notes and FAQs have some highly useful information for anyone writing code for the MSCAN (Motorola Scalable Controller Area Network) module. Although they were written for other devices, most of this information does apply to the DSP56F80x MSCAN module, especially regarding how the interrupts should be handled. I found that the DSP56F80x User's Manual didn't have enough details on how the error interrupts should be handled. AN2283/D Motorola Scalable Controller Area Network (MSCAN) Interrupts AN1798/D CAN Bit Timing Requirements AN2255/D MSCAN Low-Power Applications EB181/D FAQs - M68HC05 Family MCAN Module You can get the above documents by following these links: http://e-www.motorola.com/brdata/PDFDB/docs/AN2283.pdf http://e-www.motorola.com/brdata/PDFDB/docs/AN1798.pdf http://e-www.motorola.com/brdata/PDFDB/docs/AN2255.pdf http://e-www.motorola.com/brdata/PDFDB/docs/EB181.pdf Motorola has many links to Application Notes for the DSP56F80x DSP chips, just go to their website at: http://e-www.motorola.com/webapp/sps/site/homepage.jsp?nodeIdM0ylgz6wY Then select the chip you are using (for example, DSP56F807): - In the Search area (top right) enter DSP56F807 and press Go - Click on the link to "DSP56F807 Product Summary Page" - On this page scroll down to "DSP56F807 Documentation" - You will see a section titled "Application Note", this has links to all the Application Notes that apply to the DSP56F807 chip I hope this information is helpful to you. Regards, Art Johnson Senior Systems Analyst PMC Prime Mover Controls Inc. 3600 Gilmore Way Burnaby, B.C., Canada V5G 4R8 Phone: 604 433-4644 FAX: 604 433-5570 Email: http://www.pmc-controls.com -----Original Message----- From: Wang dawei [mailto:] Sent: Thursday, December 19, 2002 5:42 PM To: Subject: [motoroladsp] About CAN's least Baudrate ! Hi everybody; I am using the CAN bus. To be compatible with old communication products. I need the to run the CAN at 5-100k baudrate. But with the IPBUS clock, the least baudrate is 40M/28*64>20k. Any comments appreciated! I am using 56F807 Many thanks; _________________________________________________________________ нʹ MSN Messenger: http://messenger.msn.com/cn _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: To Post: To Leave: Archives: http://www.yahoogroups.com/group/motoroladsp More Groups: http://www.dsprelated.com/groups.php3 ">http://docs.yahoo.com/info/terms/ |