How many UARTS can be accessed in BB-black

GoogleGroups
1

Hi All,

I am pretty new to BB-black. I looked at the BB-black manual and it stated that
BBB has at least 4 UARTS. But when I look it further, due to the pin mux, one
can only access two UARTS at a time. Is this true? If I connect two UART devices
to the BBB, I will have no more UART to use? I would like to connect two
UART devices and still have two more UARTs for other use. Do I have a solution
to this problem?

Thanks in advance

Everett

2

There's 6 UARTs on AM335x, of which 5 are available for use on
BeagleBone (black or white). You can use any of them, they all work
fine.

You may run into conflicts in pin-mux desires if you want to use the
HDMI or other video display output, though. You're welcome to not run a
display in order to get access to all 5 of the UARTs that are available.

For pin-mux help, see:
https://github.com/bradfa/beaglebone_pinmux_tables

-Andrew

3

在 2013年7月19日星期五UTC-7上午4时36分30秒，Andrew Bradford写道：

I am pretty new to BB-black. I looked at the BB-black manual and it
stated
that
BBB has at least 4 UARTS. But when I look it further, due to the pin mux,
one
can only access two UARTS at a time. Is this true? If I connect two UART
devices
to the BBB, I will have no more UART to use? I would like to connect two
UART devices and still have two more UARTs for other use. Do I have a
solution
to this problem?

There’s 6 UARTs on AM335x, of which 5 are available for use on
BeagleBone (black or white). You can use any of them, they all work
fine.

You may run into conflicts in pin-mux desires if you want to use the
HDMI or other video display output, though. You’re welcome to not run a
display in order to get access to all 5 of the UARTs that are available.

For pin-mux help, see:
https://github.com/bradfa/beaglebone_pinmux_tables

-Andrew

Hi Andrew,

Thanks for the quick answer.

Luckily I don’t need to use any display. I have checked the pin-mux thing from your
link and hardware manual of BBB. From what I can see, it seems that only in some
modes, portin of the UARTs are exposed. UART5, for example, has TX and RX on
pin 37 and 38 on P8 header under mode 4. But under mode 4, no other UARTs
are exposed. There is no mode available that can exposed more than 1 UART
(just TX and RX) from P8 and P9 expansion headers. Doesn’t it mean only one
UART can be used (apart from the debug uart)?

Thanks,

Everett

4

Mode settings are per pin.

Gerald

5

Sorry to disturb, I seem to remember chip TRM mentioning some restrictions on multiplexing. I do not remember exact place or words used, but I assumed you are not totally free on muxing. The way I understood you must use the same mux mode for all pins of the same device. So you can not choose mux ie I2S2_SCL in mode 3 on D17 pin and have I2C2_SDA in mode 2 on A14 pin. Just curious…

6

I have a little experience with this board and you can set them based on a pin by pin basis.

Gerald