PRU UART pins - where?

General Discussion
1

Hello,

The PRU Cookbook has two examples for using PRU UART: PRU Cookbook
It seems they are using Serial Debug Header for PRU UART i/o (there’s a picture showing this header where the FTDI cable should be attached). But they configure P9_24 and P9_26 pins to pru_uart mode.
I built and uploaded the firmware to the PRU and ran it. When I connected my FTDI cable to the Serial Debug Header, I saw only Linux console login prompt.
I couldn’t readily connect my FTDI cable to P9 header as they are both female.
Is there any way to get PRU UART i/o on the Serial Debug Header of the BBB, or is it just the mistake in the PRU Cookbook?

2

No answer here?

I never used a PRU debugger, nor did I read the Cookbook.

But when I need to connect two femals I use such long board connectors

moving the black bar to the middle.

3

Ok, I assumed there was a typo in the Cookbook and used the P9_17 and P9_18 pins for PRU UART.

4

If you check the BBB system reference manual [1], sheet 4 shows the Rx and Tx pins on the FDTI connector are connected to the P9_24 and P9_26 pins.

–Mark

[1] beaglebone-black/BBB_SCH.pdf at master · beagleboard/beaglebone-black · GitHub

5

They are not. According to the schematic, FTDI connector goes to CPU’s UART 0, while P9_24 and P9_26 are UART 1.

6

Oops, I stand corrected.

Oddly, the P9 header table[1] shows that both P9_17/P9_18 and P9_24/P9_26 should work.

–Mark

[1] http://exploringbeaglebone.com/wp-content/uploads/2019/01/533160-c06f009.png

7

It will work, it’s just that PRU UART and CPU debug UART are not the same. So you can’t use Serial Debug Header to debug PRU, it seems.

8

Just be aware that P9-24, P9-26 are also DCAN1 and the only CAN port available if you are using cape EEROMs which use I2C instead of DCAN0. One of the LCD capes I bought that that problem. They could have used a different I/O for the buttons but instead used one of the CAN pins which made it useless for a remote CANopen display and control panel.