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Downloading and Running a Program->Establishing Communication with the Target Board
Before the Debug Configuration dialog box is displayed, the debugger has established communication with the BDM on the target board.
It first looks for an available FireFly on a USB port. If it does not find one it will attempt to use a parallel port interface.
To do this, it first reads the BIOS data area to determine the register addresses of available parallel ports. It then checks each in turn until it finds one with power on the BDM power pin. It then attempts to synchronise communication with the BDM on this parallel port. If it succeeds, it halts the CPU on the target board, reconfigures the BDM configuration status register so that the HALT instruction is not a privileged instruction and determines the number and type of hardware breakpoints available using the BDM revision level information. If it fails to synchronise communication, the debugger tries the next parallel port (if available).
It has been found that on the M5249C3 board under some circumstances BDM communications appears to be synchronised but the BDM configuration status register cannot be read. If this happens, the debugger will request permission to reset the target board. After a reset, the BDM will behave normally.
Note that some PC's do not correctly configure the BIOS data area and so if it reports that there are no parallel ports you will be offered the chance to choose a parallel port address.