Cmod A7-35T Board maximum USB communication speed to windows PC.

[Bryan Reeves]

I've used a lot of s6 boards in the past, and I'm currently switching from the S6 to the A7 cmod (as I can't buy the S6 anymore).  The S6 however had a faster and better interface to the USB chip than the A7 allowing communication via the EPP mode. 

What is the fastest rate at which you can drive the UART_TXD_IN and UART_RXD_OUT pins?  I was wanting to get at least 1Mbps off the board (preferably 12Mbps).  

For 12MBaud can this be done with the Digilent Adept software interface or do I need to go to the D2xx drivers from FTDI?

Edited July 21, 2023 by Bryan Reeves

[zygot]

6 hours ago, Bryan Reeves said:

For 12MBaud can this be done with the Digilent Adept software interface or do I need to go to the D2xx drivers from FTDI?

Most USB UART bridge devices top out at 3 Mbaud. The FTDI devices with an "H" can do 12 Mbaud using D2XX drivers.

You might find this tutorial interesting: https://forum.digilent.com/topic/24531-debugging-with-the-ftxxxx-mini-modules/

FTDI has a number of application notes that help explain the usage of of the VCP and D2XX drivers. Most OSes enumerate USB Bridge devices as COM or TTY devices which have a limited range and number of supported baud rates.

[JColvin]

Hello,

It is also worth noting in anticipation for any follow up that it is not possible to use the synchronous, or any, FIFO mode on the Cmod A7. Sections 3.1.4.2 and 3.1.4.3 in the FTDI FT2232HQ datasheet, https://ftdichip.com/wp-content/uploads/2020/07/DS_FT2232H.pdf, describe that many pin connections are needed to facilitate these modes. 

However, as per the Cmod A7 Reference Manual, https://digilent.com/reference/programmable-logic/cmod-a7/reference-manual#usb-uart_bridge, these connections are not facilitated, with only 4 JTAG pins and a single RxD/TxD pair connecting the FTDI chip and the Artix 7 FPGA. Therefore, you will be limited to the theoretical 12 Mbaud over UART as FTDI advertises on their feature list for the component: https://ftdichip.com/products/ft2232hq/.

Note that there is latency built into the FTDI drivers, https://www.ftdichip.com/Documents/AppNotes/AN232B-04_DataLatencyFlow.pdf, so this theoretical data rate will realistically be around 1 Mbaud with the default FTDI drivers. You might be able to get higher rates from the tutorial @zygot linked as well finding these other threads worth a read:

• https://forum.digilent.com/topic/17096-busbridge3-high-speed-ftdifpga-interface/
• https://forum.digilent.com/topic/22194-how-can-i-maximize-the-uartlite-baud-rate-beyond-921600-baud/
• https://forum.digilent.com/topic/16547-need-help-fast-connection-fpga-pc/
• https://forum.digilent.com/topic/2682-uart-communication-control-with-cmod-a7/

Thanks,
JColvin