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.
Best Answer
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".