I'm a beginner in the MCU world, I've been looking at some comparison tables for MCU capabilities and I am a little confused about USB capabilities.

For instance, looking at this Microchip listing https://www.microchipdirect.com/Chart.aspx?branchId=2155&mid=14&treeid=21, MCUs' USB support is always advertised as one of these 4 possibilities: "None", "Full Speed", "Host, Device", or "High Speed".

But none are advertised as "High Speed Device AND Host", not even the $10 ones when for less than $2 you get similar models supporting Device+Host and for less than $3, high speed. And when I look at the capabilities of an ATSAM3U1C, (https://www.microchip.com/wwwproducts/en/ATSAM3U1C#additional-features) for example, high speed capabilities are mentionned, but not USB Host support.

I wonder if it's exclusive, or if it's my current ignorance of the field that's kicking in and that, perhaps through knowledge of the USB protocol, it should be implicit that USB High Speed device support necessarily comes with USB (full speed, at least) Host support and it is therefore not mentionned. Could you please shed some light on this ? Thanks.

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    \$\begingroup\$ This is really about Microchip's rather vague definitions in a summary document, which is probably what they consider the most significant aspect - you'd need to look at the individual datasheets to see exactly what each MCU can do. For instance, one that just says "Full Speed" in the summary says "One full-speed (12 Mbps) Universal Serial Bus (USB) 2.0 interface/Embedded host and device function/Eight endpoints" in the datasheet. \$\endgroup\$
    – Finbarr
    Jan 2 at 15:55
  • \$\begingroup\$ There are plenty of device-only USB-HS intefaces on the market. \$\endgroup\$ Jan 2 at 16:37
  • \$\begingroup\$ Thanks, it's indeed on Microchip's listings being incomplete or inaccurate. In fact, It'd seem the first MCU with HS Host USB support on that list is the ATSAMS70J19. There was no mention of an MCU supporting HS Device and FS Host from what I could tell. Also, the quality of that list is honestly baffling, some of the microcontrollers advertised as "High Speed" USB in the list don't even support high speed USB according to the datasheet. \$\endgroup\$ Jan 2 at 17:29

USB High Speed device support necessarily comes with USB (full speed, at least) Host support

Absolutely NO. "Device support" and "Host support" are two entirely different functions and require different hardware blocks. HS (high-speed 480 Mbps) USB Host support requires probably 10 times more resources than a "HS device". That's why you rarely find two HS USB controllers, HOST controller, and DEVICE controller in a cheap low-end MCU. Only medium-to-high end MCU can afford HS host support, which also requires significant intelligence on software side and system memory resources. So a MCU with "USB HS Host support" are in totally different class.

The MCUs that have host and device functions (usually multiplexed into the same set of connector pins) are frequently dubbed as "OTG", a largely meaningles moniker "On-The-Go". Nowadays it is called "Dual-Role USB port".

  • \$\begingroup\$ Very clear answer, ty. If it adds to your point for people looking at this question, I wrote down the lowest 5K price for ATSAM devices with USB support: $0.83FS, $1.63FSHost, $2.34HS, $5.57HSHost. If I may ask one more thing, you say host and device functions are usually multiplexed - are there MCUs where they are not multiplexed, and able to run in parallel so as to avoid using 2 MCUs and with a price similar to entry-level USB host or device MCUs ? If so is there a specific term, keyword, that I could use to find them ? I'm wondering how I could achieve parallel host/device functionality. \$\endgroup\$ Jan 9 at 17:32
  • \$\begingroup\$ @JulienBERNARD, there are several processors with independent host/device function. Quick search within Texas Instruments portfolio of Sitara processors, AM3352, shows support for TWO "DRD" ports. Obviously one port can be configured as Host, and the other as Device.$4.72 in 1k qty.AMIC110 is $4 \$\endgroup\$ Jan 9 at 20:06

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