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Can someone suggest a manufacture for a crystal or oscillator in the 16 MHz range? We usually buy our crystals/oscillators from Murata and they have a 12 week lead time. Thanks, Janet Lefko Electrical Engineer Tekscan, Inc. 617 464-4500 -----Original Message----- From: Andrew Lohmann's New Email Server [mailto:] Sent: Wednesday, February 25, 2004 3:56 AM To: Subject: Re: [68HC12] HCS12 Oscillator circuit frequency Hi, Some of the S12's include a pre-loaded bootloader, so the lower clock speed which affects down load time could be mittigated by programming lot's of target's at one time surely? The advantage of using the lowest practicle crystal frequency, and the lower power Colipits oscillator configuration is that potentially troublesome harmonics of the crystal frequency that could be radiated are minimised. I get 15,974,400Hz from 3,686,400 Hz (crystal) / 3 * 13. I picked the lowest convenient frequency that suits RS232 baudrate generation. As too the speed change, I think the P&E with Cosmic Zap programmes at initial bus speed. You you would probably need to BDM load a small bootloader which configured the pll and switched speed before downloading the bulk of your application by serial or whatever. To acheive that in most cases? Andrew Lohmann AIIE Design Engineer PLEASE NOTE NEW EMAIL ADDRESS IS: Bellingham + Stanley Ltd. Longfield Road, Tunbridge Wells, Kent, TN2 3EY, England. Tel: +44 (0) 1892 500400 Fax: +44 (0) 1892 543115 Website: www.bs-ltd.com ----- Original Message ----- From: Oliver Betz To: Sent: Tuesday, February 24, 2004 4:57 PM Subject: Re: [68HC12] HCS12 Oscillator circuit frequency *** This e-mail has been modified by Finjan's Vital Security for E-Mail. *** More details can be found in the attached file, Vital Security Notification.html Robert Imhoff <> wrote: > How does one choose the optimal crystal frequency for the HCS12 (e.g. > MC9S12DG256)? With 4MHz...8MHz, you can use rather large capacitors without overloading the crystal (or the oscillator amplifier), therefore parasitic capacitance doesn't influence the design and you get a pretty stable and reliable oscillator. Lower frequencies make the PLL response slower and probably cause more jitter. Initial BDM speed is very low. > Was wondering with Andrew Lohman, why do the evbs like the one from > Technological Arts or CardS12 from Elektronikladen use 16 MHz crystals, maybe to achieve good BDM speed. Most BDM Flash programming stuff can't use the PLL. Gordon's programmer can (IIRC), iSYSTEM can't. What about Nohau, P&E? Oliver -- Oliver Betz, Muenchen --------------------To learn more about Motorola Microcontrollers, please visit http://www.motorola.com/mcu o learn more about Motorola Microcontrollers, please visit http://www.motorola.com/mcu ------ > . |
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HCS12 Oscillator circuit
Started by ●February 22, 2004
Reply by ●February 25, 20042004-02-25
Reply by ●March 1, 20042004-03-01
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At 17:57 24/02/2004 +0100, Oliver Betz <> wrote: > > Was wondering with Andrew Lohman, why do the evbs like the one from > > Technological Arts or CardS12 from Elektronikladen use 16 MHz crystals, > >maybe to achieve good BDM speed. Most BDM Flash programming stuff >can't use the PLL. > >Gordon's programmer can (IIRC), iSYSTEM can't. > >What about Nohau, P&E? > >Oliver The Nohau BDM can do that as well - namely to engage the internal HCS12 PLL in order for the Flash and EEPROM Programming to be faster using higher higher speed BDM communication. My colleague Steve Russell tells me that when programming Flash and EEPROM at 4MHz and at 25MHz bus speeds, the programming speed is almost proportional to the ratio 25 / 4, so the speed increase is significant. This is done in the Emulator Configuration window by specifying values for the Loop Divider and the Reference Divider registers, and checking the "Pll In Use" check-box. Then when programming the Flash or EEPROM (or both), the BDM Resets the CPU, programs the internal PLL to the specified values and engages it to up the BDM communication speed, and then finally programs the Flash and EEPROM using higher speed BDM communication. The programming clock is set in any case to 150 KHz - 200KHz, but the BDM communication which transfers the programming data is faster this way. Hope this helps, Doron Nohau Corporation HC12 In-Circuit Emulators www.nohau.com/emul12pc.html |
