USB to UART Bridge IC question

[AbhinavRajan]

I have a few basic doubts regarding this USB to UART bridge IC - XR21B1424 - https://www.maxlinear.com/ds/xr21b1424.pdf

My questions are just from the hardware perspective.

1. This IC converts USB protocol to UART protocol at the available 4 output channels, right? Is there any software within the IC that will do this conversion of protocol or do we have to write separately - connected to the Host USB side? Like, what should a hardware person keep in mind while using the IC - Like, just connect differential lines on Input and take 4 Tx,Rx lines on the output connected appropriately to the Micro or SOC or whatever IC?

2. If I have one USB 2.0 running at 480Mb/s connected as the input, how is speed and addressing done for each channel? Will all output UART channels operate at the same speed? What happens if two output channels require value from USB at the same time?

 

[stenzer]

Hi,

I have a few basic doubts regarding this USB to UART bridge IC - XR21B1424 - https://www.maxlinear.com/ds/xr21b1424.pdf

My questions are just from the hardware perspective.

1. This IC converts USB protocol to UART protocol at the available 4 output channels, right? Is there any software within the IC that will do this conversion of protocol or do we have to write separately - connected to the Host USB side? Like, what should a hardware person keep in mind while using the IC - Like, just connect differential lines on Input and take 4 Tx,Rx lines on the output connected appropriately to the Micro or SOC or whatever IC?

According to the description on page 14, you may have to configure the IC depending on your used MCU connection. To operate the USB interface provided by your e.g. MCU, you should have a look at ist clock requirements, as the internal (RC) oscillator might not be stable enough to be used as a reference for the required USB clock of 48 MHz.

At power-up, the XR21B1424 will default to 115.2 kbps, 8 data bits, no paritybit, 1 stop bit, and no flow control. If a standard CDC driver accesses the XR21B1424, these defaults will be changed. See“Device Driver” on page11

2. If I have one USB 2.0 running at 480Mb/s connected as the input, how is speed and addressing done for each channel? Will all output UART channels operate at the same speed? What happens if two output channels require value from USB at the same time?

The IC only supports USB 2.0 Full-Speed (12 Mbps). USB 2.0 High-Speed (480 Mbps) is not supported, so you have to configure your MCU appropriately.
The UART speed can be configured by you, by means of the baud rate. According to the "CDC_ACM_IFSET_LINE_CODING" command at page 20 it seems to be possible to set an individual baud rate for each channel. Have a detailed look at the available commands. UART uses flow control which is available for each channel (see UART pins RTS & CTS). Further, each channel provides a 512 byte RX FIFO buffer and a 512 byte TX FIFO buffer for handling simultaneous requests by meaning of a temporary buffering of the TX and RX data.

greets

 

[KlausST]

Hi,

I assume you did not read the datasheet thoroughly.

Is there any software within the IC that will do this conversion of protocol

I assume it is a pure hardware solution. But indeed it does not matter for the IC side, it behaves like written in the datasheet.
Or maybe I misunderstood your question..

For the Host side: On first page of the datasheet it mentiones drivers for various OS. Further in the datasheet even more detailed.

Hardware:
On first page of the datasheet there is the raw block diagram.
Then there is a more detailed block diagram, some more detailed wiring diagram, and a description for every single pin?
What more do you need?
Various application notes, a user guide, an evaluation board with documentation and other documents can easily be found on the manufacturer's internet pages.

And for sure it depends on the requirements of the UART partners (SOC..) you need to read the datasheets, too. Especially about I/O levels and timing.

2)
Datasheet says:

Set the UART baud rate, parity,
stop bits, etc. Channel #0, 2, 4,
6 for channel A, B, C, D,
respectively.

For sure you can select baud rates individually for each channel...

All the data handling will be made by the Host driver and the IC...don't worry about this.

*****
It seems you want high data rate, so why do you want to use the "bottleneck" UART. Why not parallel?

You may have a look how other vendors build their USB-To-xx bridges.
Like on ftdichip.com. Without saying they are better or worse...just as additional information/idea.


Klaus