http://forums.leaflabs.com/topic.php?id=12403 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:17:32 +0000 http://bbpress.org/?v=1.0.2 q http://forums.leaflabs.com/search.php http://forums.leaflabs.com/topic.php?id=12403#post-27163 Sat, 22 Jun 2013 16:12:34 +0000 gbulmer 27163@http://forums.leaflabs.com/ <p>stephanschulz - It might be helpful to add that that device appears to like a nominal 5V power supply.<br /> At that voltage, its spec says its input pins would like a minimum of 0.7*5V = 3.5V.<br /> It's signal pins could be driven directly at a slightly lower voltage, e.g. a Maple output pin. Certainly try it, but it might be a bit sensitive to electrical noise.</p> <p>So the pins could be driven by 5V tolerant pins, using pull-up resistors to reach 5V, and set up with pinMode OUTPUT_OPEN_DRAIN.<br /> AFAICT, the SPI input signals need to rise and fall reasonably quickly (i.e. 200ns), so relatively small pull-up resistors would be needed.</p> <p>Some of the Maple SPI pins are <strong>not</strong> 5V tolerant.<br /> So, for example D11 (SPI MOSI) and D13 (SPI SCK) are not 5V tolerant, and if they have a bit of a problem driving that chip directly, they couldn't be pulled up to 5V with pull-up resistors.<br /> D32 (SCK) and D34 (MOSI) might be better because they are 5V tolerant, so you could try directly driving L9822 pins, or using pull-up resistors.</p> <p>It looks like all the SPI signals need have 'slower' rise time, or fall time than 200ns.<br /> The Maple GPIOs are normally set up for a 50MHz rise/fall, so if there are problems, it might be worth having a look at <code>gpio_set_mode</code> and setting the rise/fall time a bit slower.<br /> For example <code>GPIO_CR_CNF_OUTPUT_OD | GPIO_CR_MODE_OUTPUT_10MHZ</code> or even <code></code>GPIO_CR_CNF_OUTPUT_OD | GPIO_CR_MODE_OUTPUT_2MHZ`<br /> WARNING: I've never tried this!</p> <p>The L9822 looks very tolerant to being driven at low speed. AFAICT, it has no lower speed.<br /> So you could write a simple 'shift_out' function using two digital pins, and just setting them with digitalWrite. This might be useful if you haven't got an oscilloscope, or have problems with SPI. Using a 'soft-SPI' would allow the bits to be written so slowly that LEDs could be wired up the the soft-SPI-equivalent signals, or <code>print/println</code> could be used, and you could see what is happening. The pins would be set up for pinMode OUTPUT_OPEN_DRAIN.</p> <p>A small aside; that chip could be 'emulates' using an ordinary, cheap 8bit SIPO shift register ($0.50) driving LEDs. Judicous choice of part would work at 3.3V too, so you could do software development and testing without a 5V power supply.</p> <p>Tiny aside: the L9822 is listed as obsolete e.g. a Mouser, but the L9822E is active, so I assume that's the part about to be used. </p> http://forums.leaflabs.com/topic.php?id=12403#post-27123 Fri, 21 Jun 2013 13:10:49 +0000 mlundinse 27123@http://forums.leaflabs.com/ <p>Its all in the datasheet so its good to practice how to read them, sure<br /> they can be anything from clear and easy to understand to completly confusing<br /> and filled with errors.</p> <p>You will not be sure until you have tried it out, but from what I can see<br /> it is MSB, clock idling low, data capture on first clock transition, that would be<br /> Spi Mode 0, and max clock frequency of 2MHz. </p> <p>The maximumum clock frequency also depends upon the amount of noise in the system<br /> and length and capacitance of connecting leads. So start with a low clock and<br /> increase it. If you have an oscilloscope you can watch the waveforms as you increase<br /> spi clock frequency. </p> http://forums.leaflabs.com/topic.php?id=12403#post-27113 Fri, 21 Jun 2013 09:23:08 +0000 stephanschulz 27113@http://forums.leaflabs.com/ <p>i am planning to use this smart solenoid driver <a href="http://www.st.com/web/en/resource/technical/document/datasheet/CD00000110.pdf" rel="nofollow">http://www.st.com/web/en/resource/technical/document/datasheet/CD00000110.pdf</a></p> <p>but i am uncertain how to use the maple's spi library to communicate with this chip</p> <p>can anyone take a look at the documentation and tell me which mhz, which mode etc to select?</p> <p>thanks so much.<br /> stephan </p>