Question about using Pmod USB UART module

[conanandai100]

Hi,

I am trying to use Pmod as UART to dump out some data from logic side of Zedboard, so I bought the Pmod USB UART module from digilent and connected it to Pmod JA (pretty sure my constraints are correct). My project worked perfectly before when I was using Spartan-3E and Nexys 2, both have a simple UART interface. I thought this module should work as well, but it didn't respond when I launched UART command from my python terminal by some reasons. I checked the specification: https://www.digilentinc.com/Pmods/Digilent-Pmod_ Interface_Specification.pdf then. The only difference is that there is no CTS or RTS in my project, but both are reserved on the UART module. I tried to disable them or set to low but not working. As it is said that CTS and RTS are optional in the pdf, I am trying not to modify my code which could lead to more issues. Is there anything I need to know when using this UART module? Or a demo to quickly verify how it work.

Thanks!

[zygot]

The PMOD UART is an RS-232 interface. The logic levels and cabling are completely different than USB UART interfaces. For RS-232 the Tx and Rx wires can be switched in the cable making it very confusing. RS-232 has connectors with different numbers of pins, gender changers to switch Tx and Rx signals, lower baud rates, and a host of other variables to cause heartache and misery. I haven't seen a modern PC with a true RS-232 serial port for years.

Personally, when I need to add a UART I use a cheap TTL USB UART cable or breakout module from Adafruit or Sparkfun. You just need two spare IO pins to get reliable 921600 baud or higher connectivity to a PC and the direction of those pins is often confusing enough.