Is on board serial port has anything to do with HDMI display?

Hi guys,

I have Beagleboard XM. I am not getting the purpose of on board serial port. When i removed the serial cable from host PC, my HDMI monitor (separate) is not showing anything but My board boots up nicely. When i connect serial cable between host and Beagleboard then only it display on monitor. Can somebody help me to understand why this is happening?


Ideally their should not bee any dependency… are you setting bootargs while booting or booting from command line. What are the boot args you are passing to the Linux kernel ?

Thanks for the reply. I am not setting any bootargs while booting from command line. It takes default setting.


This is my default boot arguments.

setenv bootdelay 1
setenv loadaddr 0x82000000
setenv dvimode ‘hd720’
setenv vram ‘12M’
setenv mem ‘mem=99M@0x80000000 mem=128M@0x88000000’
setenv defaultdisplay ‘dvi’
setenv loadbootscript ‘fatload mmc 0 ${loadaddr} boot.scr’
setenv bootscript ‘echo Running bootscript from mmc …; source ${loadaddr}’
setenv loaduimage ‘fatload mmc 0 ${loadaddr} uImage’
setenv mmcroot ‘/dev/mmcblk0p2 rw’
setenv mmcrootfstype 'ext3 rootwait
setenv mmcargs ‘setenv bootargs console=${console} vram=${vram} omapfb.mode=dvi:${dvimode} omapdss.def_disp=${defaultdisplay} root=${mmcroot} rootfstype=${mmcrootfstype} ${mem}’
setenv mmcboot ‘echo Booting from mmc …; run mmcargs; bootm ${loadaddr}’
setenv nandroot ‘/dev/mtdblock4 rw’
setenv nandargs ‘setenv bootargs console=${console} vram=${vram} omapfb.mode=dvi:${dvimode} omapfb.debug=y omapdss.def_disp=${defaultdisplay} root=${nandroot} rootfstype=${nandrootfstype}’
setenv nandboot ‘echo Booting from nand …; run nandargs; nand read ${loadaddr} 280000 400000; bootm ${loadaddr}’
setenv bootcmd ‘if mmc init; then if run loadbootscript; then run bootscript; else if run loaduimage; then run mmcboot; else run nandboot; fi; fi; else run nandboot; if’


what if you connect the board with your PC by some other cable? Just
check if it's a Ground issue

Thanks Maxim for your reply, you are correct it is ground issue. now I have connected usb to miniusb cable between PC and Board, and removed serial cable. There also same problem, when I removed usb to miniusb cable from board, display does not show anything.

Thanks & Regards,



You need to contact Gerald about this problem

Use a grounded DC supply that is connected to the same ground (power strip) as the PC. Something I have said for many years now. I know of no way to create a wireless ground connection. Without the common grouns, the over voltage protection circuit goes crazy.


Then how can I make my Beagleboard as a standalone system, without taking ground from PC?? Is there any way?? Why cant it is using on board ground for the same??



Don’t tie anything to it that has its own ground! Keep the entire system floating.