# VOXL B2B Port connections questions

Source: https://forum.modalai.com/topic/635/voxl-b2b-port-connections-questions
Category: Flight Core and Legacy VOXL (https://forum.modalai.com/category/9/flight-core-and-legacy-voxl)
Tags: voxl
Posted: 2022-01-05 14:12:22 UTC by amitga
Replies: 7 · Views: 1655

## amitga · 2022-01-05 14:12:22 UTC

Hi.
I was reading this:
https://docs.modalai.com/voxl-datasheets-connectors/#j13-expansion-b2b-connection
and wanted to make sure I understood corrrectly:
There are 2 I2C ports/buses available on this connector (J13 - B2B) ?
If so, can one be used as an I2C master/host, and the other as a slave (for use with external master) ?

Also, I haven't seen any information about PWM outputs. Does the VOXL have any hardware PWM outputs? If so, on which pins?

Thanks.

## Reply by Chad Sweet (ModalAI staff) · 2022-01-05 22:49:11 UTC

Yes, but to use the B2B connector you will need a custom PCB.

There are other i2c available.

There are no HW PWM on VOXL, but on VOXL Flight there are HW PWM through the Flight Core portion

## Reply by amitga · 2022-01-06 08:48:27 UTC

Thanks for your reply.
Yeah, I was planning on breaking out the B2B connector to a PCB for dev purposes.

So I shouldn't have any problems using the two I2C ports (on as master and other as slave) on the B2B, correct?

Also, if I want to do SW based PWM, is there any GPIO pin on the B2B that you would recommend using, or can I choose any free GPIO pin ?

## Reply by Eric Katzfey (ModalAI staff) · 2022-01-06 17:13:29 UTC (in reply to amitga)

@amitga The i2c ports on Voxl only support host mode, not slave mode. Also, we have never tested any i2c ports coming over the B2B connector and cannot say for sure whether they are even enabled in the system image.

## Reply by amitga · 2022-01-26 14:01:00 UTC (in reply to Eric Katzfey)

@Eric-Katzfey Thanks for the reply.
Is this a hardware limitation (i2c ports being host only) ?
Are there any plans to enable i2c in slave mode on the VOXL ?

## Reply by Eric Katzfey (ModalAI staff) · 2022-01-26 16:39:35 UTC (in reply to amitga)

@amitga Yes, it is a hardware limitation.

## Reply by amitga · 2022-01-27 14:19:56 UTC

OK.
So what about SPI or UART on the B2B connector?
Are they available and supported in OS/SW? If so, what modes does the SPI support (master/slave) ?
What baudrate does the UART support? 

Thanks.

## Reply by Eric Katzfey (ModalAI staff) · 2022-01-27 18:03:39 UTC (in reply to amitga)

@amitga The only thing we use over the B2B on our add-on boards is USB 2.0 and some GPIO. If you give us some idea of what you are trying to accomplish we may be able to offer some suggestions.