{"id":1269,"date":"2013-12-18T13:34:43","date_gmt":"2013-12-18T13:34:43","guid":{"rendered":"https:\/\/ibex.tech\/resources\/?p=1269"},"modified":"2022-07-21T12:59:18","modified_gmt":"2022-07-21T11:59:18","slug":"smbus-general","status":"publish","type":"post","link":"https:\/\/ibex.tech\/resources\/geek-area\/communications\/smbus\/smbus-general","title":{"rendered":"SMBus General"},"content":{"rendered":"\n<p>Referred to as:<\/p>\n\n\n\n<p>System Management Bus<br>SMBus<br>SMB<\/p>\n\n\n\n<p>Commonly found on computer motherboards for communication with the power source, battery charging, etc.<\/p>\n\n\n\n<p>Based on I2C&nbsp;bus:<\/p>\n\n\n\n<p>Clock frequency range 10kHz to 100kHz (a minimum is specified as SMBus has a timeout feature).<\/p>\n\n\n\n<p>Voltage levels and timings are more strictly defined than for I2C, but devices using the two interfaces can often successfully mixed on the same bus.<\/p>\n\n\n\n<p>Allows for bus VDD ranging from 3V to 5V.<\/p>\n\n\n\n<p>ACK and NACK there are some differences to be aware of when designing your software driver.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">Pull Up Resistors<\/h4>\n\n\n\n<p>SMBus voltage levels are specified with different currents compared to the I2C bus. SMBus specifies a min\u00a0sink current of 100\u00b5A, and a maximum of 350\u00b5A, compared to 3mA for the I\u00b2C bus. This determines the lowest acceptable value of the pull-up resistor:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>           3V VDD      5V VDD\nI2C Bus    > 1k     > 1.6k\nSMBus      > 8.5k   > 14k<\/code><\/pre>\n\n\n\n<p>In reality, it&#8217;s not unusual to find pull-up resistor values in SMBus systems which are lower than allowed by the specification. A popular range for pull-up resistor values seems to be 2.4K\u00a0to 3.9K<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">Good Resources<\/h4>\n\n\n\n<p><a href=\"http:\/\/www.maximintegrated.com\/app-notes\/index.mvp\/id\/476\">Maxim&nbsp;Comparing the I\u00b2C Bus to the SMBus<\/a><\/p>\n\n\n\n<h4 class=\"wp-block-heading\">PMBus<\/h4>\n\n\n\n<p>New standard enhancing SMBus to allow identifying of device functionality, etc.<\/p>\n\n\n\n<p>Extends Clock frequency range to 400 kHz.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Referred to as: System Management BusSMBusSMB Commonly found on computer motherboards for communication with the power source, battery charging, etc. Based on I2C&nbsp;bus: Clock frequency range 10kHz to 100kHz (a minimum is specified as SMBus has a timeout feature). Voltage levels and timings are more strictly defined than for I2C, but devices using the two [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[79],"tags":[],"class_list":["post-1269","post","type-post","status-publish","format-standard","hentry","category-smbus"],"_links":{"self":[{"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/posts\/1269","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/comments?post=1269"}],"version-history":[{"count":5,"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/posts\/1269\/revisions"}],"predecessor-version":[{"id":2537,"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/posts\/1269\/revisions\/2537"}],"wp:attachment":[{"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/media?parent=1269"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/categories?post=1269"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibex.tech\/resources\/wp-json\/wp\/v2\/tags?post=1269"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}