http://forums.leaflabs.com/topic.php?id=1068 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:21:04 +0000 http://bbpress.org/?v=1.0.2 q http://forums.leaflabs.com/search.php http://forums.leaflabs.com/topic.php?id=1068#post-6821 Tue, 11 Oct 2011 13:10:37 +0000 nplayle 6821@http://forums.leaflabs.com/ <p>OK thanks guys.<br /> I was worried that my sending a dummy byte would eventually overwrite a register it should have. I have it working the as described and it works perfectly, so I'll leave it as is. </p> <p>Nick </p> http://forums.leaflabs.com/topic.php?id=1068#post-6701 Fri, 30 Sep 2011 10:22:07 +0000 robodude666 6701@http://forums.leaflabs.com/ <p>Check the datasheet of the device you're trying to communicate with. Generally speaking, you must always send a dummy byte like crenn said. The byte received then is the response from the device. The datasheet for the device you're communicating with will have a waveform diagram with an example of what bytes must be sent to receive data.</p> <p>What you've reported, however, is not a bug -- it's just the way SPI works like crenn said.</p> <p>-robodude666 </p> http://forums.leaflabs.com/topic.php?id=1068#post-6699 Fri, 30 Sep 2011 09:32:30 +0000 crenn 6699@http://forums.leaflabs.com/ <p>nplayle, that's actually the way that you use SPI, if you want data back, you need to send a 'dummy' byte which isn't used for anything. Spi.read() just returns the last byte that came into the SPI data register. </p> http://forums.leaflabs.com/topic.php?id=1068#post-6616 Mon, 26 Sep 2011 08:35:39 +0000 mbolivar 6616@http://forums.leaflabs.com/ <p>Hi Nick,</p> <p>I'll look into this. </p> http://forums.leaflabs.com/topic.php?id=1068#post-6569 Sat, 24 Sep 2011 18:10:42 +0000 nplayle 6569@http://forums.leaflabs.com/ <p>Hi all,<br /> I'm a relatively new user of the maple, so forgive me if this is a simple question.</p> <p>I'm trying to read data via the SPI bus for an accelerometer. Writing data works as expected, but using spi.read is causing me some issues. </p> <p>When I send the data address out, it uses a full byte as expected. Then I use spi.read, but the chip is no longer being clocked by the spi.write command, so no data is returned to me. Since a full read cycle takes 16 clocks, the accelerometer doesnt send data until after 8 have passed. I can cheat it by writing blank data, and then the accelerometer sends data back to me, but something tells me this isnt a good way of doing it... I'm assuming it has something to do with not detecting there are unread bytes, but I'm not sure how to tell it there are.</p> <p>Here is the code I have<br /> This works:<br /> <pre><code>      spi.write(0xE8);            spi.write(0x00);       uint8 data2 = spi.read();</code></pre> <p>This doesnt:<br /> <pre><code>spi.write(0xE8);&lt;br /&gt; uint8 data2 = spi.read();</code></pre> <p>Thanks<br /> Nick </p>