I tried asking this as a question, but it seemed to disappear.
I can’t seem to find the UART3_RXD on the headers.
For posterity:
UART1_RXD - P9 - 26 - mode0
UART1_TXD - P9 - 24 - mode0
UART1_CTS - P9 - 20 - mode0
UART1_RTS - P9 - 19 - mode0
UART2_RXD - P9 - 22 - mode1
UART2_TXD - P9 - 21 - mode1
UART2_CTS - P8 - 37 - mode6
UART2_RTS - P8 - 38 - mode6
UART3_RXD - ?
UART3_TXD - P9 - 42 - mode1
UART3_CTS - P8 - 36 - mode6
UART3_RTS - P8 - 34 - mode6
UART4_RXD - P9 - 11 - mode6
UART4_TXD - P9 - 13 - mode6
UART4_CTS - P8 - 35 - mode6
UART4_RTS - P8 - 33 - mode6
UART5_RXD - P8 - 31 - mode4
UART5_TXD - P8 - 37 - mode4
UART5_CTS - P8 - 31 - mode6
UART5_RTS - P8 - 37 - mode6
(This explains why only RX/TX is available for UART5)
But on the header pinout, I was unable to find UART3_RXD. In looking through the /sys/kernel/debug/omap_mux/ files I found that spi0_cs1.gpio0_6 mode1 should be the RXD, but still I’m unable to find where, physically, RXD is.
All the pins are not accessible. Read section 6.3.6.
6.3.6 Serial Ports
There are four serial ports on the expansion headers. UART ports 1, 2, 4 ports have
TX,Rx,RTS and CTS signals while UART5 only has TX and RX.
You will see UART3 is not listed. Due to pin usage on the board, all of the UART3 signals are not on the expansion header.
Gerald
Is UART3 accessible in any other way? Or is it useless?
It is not accesible on the BeagleBone any other way. Due t the pinmuxing and the location of these signals with other signals, the other signals were required.
Gerald
I think UART3 can be used for write only devices such as displays which only require tx data an possible RTS/CTS.
You can remove R197 and solder your Rx wire to its pad, but you’ll loose card detect signal, that is not very important as long as you tell kernel not to use it.
It seems to me that all signals are available for UART5:
UART5_RXD - P8 - 38 - mode4
UART5_TXD - P8 - 37 - mode4
UART5_CTS - P8 - 31 - mode6
UART5_RTS - P8 - 32 - mode6
Am I wrong?