Why 3 BUSES?
YABA offers the freedom of using, also simultaneously, 3 different buses via a single connector, characterized by high performance, flexibility and low cost:
USB® : in the course of the last 20 years, USB bus has evolved from a system designed to temporarily connect external devices (typically with a relatively slow connection speed) to a transport interface that today can easily compete with the fastest system buses.
EtherCAT® (or other LVDS based bus): this bus offers performances among the best between today’s available industrial buses, while keeping low development costs.
I2C/SMBUS® : has always been the protocol of choice for easy interfacing between different devices.
Developers have the option of using just one, two or all the 3 available buses simultaneously.
As explained on the concept page the hardware maker that want to apply USB logo as EtherCAT logo on their products needs registration and certifications on the respective organizations, alternately they will use already certified YABA bus module interface that found on MarketSpace or use I2C or raw LVDS protocol without any licensing issues.
The 3.1 protocol release guarantees high data transfer speed with low latency, a key factor for adopting USB as a system bus.
The USB 2 protocol has a theoretical latency of 125 uS but, because using a polling pooling architecture, realistically its performances are never below 1 ms of latency. This value is acceptable for applications activating relays or mechanical switches but unrealistic for scenarios where axis position has to be transferred via an encoder that requiring a latency of 100 uS or lower.
The USB 3.1 protocol has a theoretical latency of 1 uS. Based on laboratory tests, the real latency is between 50 and 100 uS – part of this amount is for the delays caused by the hub and the operating system. This value is in any case 10 times lower than the previous one.
With an in depth review of software and drivers it is reasonable to achieve performance below 50 uS.
The turning point: “Alternate Mode”
With implementation step, YABA will utilize the USB connector on “alternate mode”, where the additional high speed lane SSRTX2 is used as EtherCAT ®LVDS bus working at 100Mb/s with a latency of 20 uS and a jitter of 1uS.
Note that this is not an absolute constraint, developers will be able to use this lane for any communication protocol that can use a high-speed differential pair.
SBU1/SBU2 pins are used for a simple and low cost I2C serial bus with a speed of 100 Kb/s and a deterministic latency of 10ms.
USB 3.1 is retroactively compatible with the previous versions of the protocol. It will be possible to connect all devices compatible with USB 1.1, 2.0 and 3.0 with transfer speed between 1.5 Mb/s and 5 Gb/s.
I2C guarantees interfacing with many devices and microcontrollers.
EtherCAT ®can interface a lot of existing device and has become the benchmark for high-performance industrial buses.
Those who do not need this protocol can use the additional lane for other buses.
The wide spread diffusion of the USB bus guarantees a very low cost for chips and connectors.
EtherCAT ®offers the best cost/performance ratio.
I2C it is a very low cost bus if not the most economical to develop.
Why USB C connector?
USB C internal connector offers several interesting features making it a solid choice for a bus architecture with very few downsides.
This type of connector is described on USB.org and can handle USB 3.1 Gen 2, it can support a transfer speed of up to 10 Gb/s.
YABA will use the main lanes for classical USB 1.5, 2.0 and 3.1 Gen1 connections with speed up to 5 Gb/s, the secondary lane as LVDS-MBUS for EtherCAT ®transport, and the additional SBU pins for the I2C connection. All this using just a single and low cost connector.
High current carrying capacity
The USB C internal connector (also named U31G2) uses 3 high current pins for the power (plus 3 for ground) and can supply power till 3A/5V (15W) as based configuration. When used with Power Delivery standard it can supply till 5A/20V (100W). This gives a high flexibility on the range of devices that can be connected, even for the most power hungry. To give some examples, a CPU board based on Raspberry CM3 consumes approximately 5W while one based on and entry level Atom X can reach 40 W. An expansion board with 16 power relays can consume up to 10 W.
The USB C connector can instead handle them easily.
Finally, the USB C allows to power-up both host systems (YABA CPUs) and device systems (YABA expansion boards).
Good mechanical features
USB C Internal Header connectors have good mechanical characteristics. Connectors pins have to guarantee a fault-proof electrical contact and for this reason they are mechanically preloaded.
The case is shielded and have additional pins usefull for a strong fixing.
The pin spacing is 0.8 mm that is twice the spacing of standard USB C connector, this making welding easier.
Even if the pins are widely spaced compared to standard USB C connectors, USB C Internal connectors are designed to use SMT pins/pad; these connectors are not so easy to handle for the less advanced manufacturer. To solve this minor issue, one of the first products available on the YABA marketplace will be adapters and pre-mounted connectors in order to make easy soldering.
For connecting standard USB peripherals as camera, memory key etc. YABA will also provide simple passive adapter for standard external USB A and USB C connectors.
On the top of passive adapters, the marketplace will also offer active USB-Serial adapters designed for expansion boards using microcontrollers not supporting USB but only having a serial port. These kind of devices can also use the I2C bus directly and without any type of conversion.