On Fri, 1 Apr 2005 11:50:49 -0600, Glen VanMilligan wrote: > Can someone tell me how to access the second serial port on the balloon > board? > By second, I mean the one on the bottom side of the board. It's Serial port 2 (also known as the IrDA port, although you can (and should) kick the IrDA gubbins out the way). The registers are at Address Name Description 0h 8003 0000 UTCR0 UART Control Register 0 0h 8003 0004 UTCR1 UART Control Register 1 0h 8003 0008 UTCR2 UART Control Register 2 0h 8003 000C UTCR3 UART Control Register 3 0h 8003 0010 UTCR4 UART Control Register 4 0h 8003 0014 UTDR UART Data Register 0h 8003 0018 ? Reserved 0h 8003 001C UTSR0 UART Status Register 0 0h 8003 0020 UTSR1 UART Status Register 1 0h 8003 0024 ? 0h 8003 005C ? Reserved However, your OS is likely to expose the UART in a more friendly way than just handing you a pointer :) In what way is the serial port not working? Steve