THVD8000: Difference between Homebus and Powerbus

Hi Manu,

1. So there are a few significant differences between homebus and the THVD8000 (its not really a protocol - Powerbus is just using OOK modulation to couple data to the power lines). Before I list a few differences I will say we have replaced the MM1192 in applications with the THVD8000 because while the application setup is a bit different they are designed to achieve the same goal and largely have the same use cases (typically the THVD8000 is more flexible) - for some key differences please see below:

1a) Homebus is a multi-drop configuration while powerbus is multipoint. However Powerbus is based on RS-485 so it can also handle multidrop configurations.

1b) Homebus has data and power on the same bus (up to 36V) and Powerbus can also work in the same systems by sharing a power/comms bus - however Powerbus can be modified to work with AC Mains or low impedance systems - although the architecture is more complicated then. 

1c) Both systems use differential communication 

1d) Both systems use 0V differential to transmit a logic 1

1e) Homebus will invert each bit for logic 0. So if a logic zero is a high voltage - the next logic 0 transmitted is a low voltage (this is done to keep DC balance in the system) This is Alternative Mark Inversion Encoding (AMI) that is used. 

1f) Powerbus also keeps a DC balanced system by using a pulse-train of frequency fmod set on the IC itself. - So the modulation scheme is different in these systems but they both work to DC balance the bus. 

1g) Homebus is generally rated for 9.6kbaud (can be faster with the extended protocol - but generally its slow) with the original standard spec'ing up to 200m of cable with the extended mode being up to 1km.

1h) Powerbus is suggested to transmits 1/10th of the modulation frequency - so for the THVD8000 at its max modulation (5MHz) you can transmit up to 500Kbps. This is RS-485 based so it should be able to meet the 1km (but not generally at max data-rate - datarate and modulation frequency may have to decrease for up to 1km case). 

1i) When using a OSI network stack model (Where the layers are (starting at bottom)  PHY --> DataLink --> Network --> Transport --> Session --> Presentation --> Application) Homebus defines a standard for the PHY, DataLink, Network, and Application layers. This means there are Homebus defined items for how packets are structured, higher level network functions, and pre-defined high level commands. Powerbus past the PHY layer is mainly designer choice as Power bus is  largely protocol independent - this is because it is based on RS-485 which really only defines the PHY layer - this allows a bit more flexibility with the THVD8000. 

1j) Both systems use capacitors and inductors to couple data and power onto the same bus (inductors couple power / block data and capacitors couple data / block power) 

1k) Finally the most important thing is how the chips are setup - MM1192 is full-duplex whereas THVD8000 is half duplex, so if one node needs to transmit and receieve at the same time two THVD8000's would be needed per node. However since the THVD8000 is multi-point, multiple drivers can exist on the same bus so half duplex may still work. 

Generally speaking both protocols can achieve the same goal however the system needs to be either powerbus or Homebus - they don't work super well on the same line.

The real advantages to powerbus are: 

1. Faster data-rates

2. Ease of Implementation - due to being largely protocol independent there is much more flexibility in design which can help expedite design processes due to it being relatively simple.  

3. Multi-point; Multi-point drivers can support multiple drivers on the same bus - allowing for less wires - whereas in Homebus it is multi-drop which requires at least two sets of conductors so that the end points can communicate back to the host if necessary.

For your second question:

The Powerbus system is generally more simple from a higher level firmware perspective. For the physical system they are very similar so it shouldn't be a major difference in design - the passive components may need to be redesigned but we have a lot of information on how to do that (and I have attached an excel calculator that already does it for you)

 3582.THVD80x0_Design_Calculator.xlsx 

Also we have a THVD8000 design guide + the datasheet is very helpful:

Datasheet: https://www.ti.com/lit/ds/symlink/thvd8000.pdf?ts=1661786941899&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTHVD8000

Design Guide: https://www.ti.com/lit/an/slla496a/slla496a.pdf?ts=1661786963367&ref_url=https%253A%252F%252Fwww.google.com%252F

This should be the right collateral for the use case. 

However it really depends on how their system looks - if they are already using MM1192 then it shouldn't be a huge change - but there would be some rework; however I would be more than happy to help if any other questions pop up along the way.

Please let me know if you have any other questions!

Best,

Parker Dodson