I have finally got my mbed board talking SPI at 1Mhz to my propeller board, and a with a defined sync up protocol. I have chosen mode 3 (clock default to high, first clock transition to low is then the output is setup [give the slave warning]). I've for now set the data width to 16bit and it does not do any thing special, but will hopefully next week do some better VGA output. the setup is simple, as the spi clock does not run when there is no data to transfer, we wait for a clock high of more than 8000 master clock on the slave (which is about 5Khz clock delay) as the spin interpreted debug code can only cope with a comms speed of 10Khz. one we see that delay we know the next high to low transition marks the begining of the next "frame" so we send back the magic 0x8401 which the mbed is waiting for. the mbed code: /media/uploads/xenonym/prop_ser_vga.zip the properller code :/media/uploads/xenonym/propeller_firmware.zip designed to run on a propeller demo board the following pins need to be connected : mbed gnd -> prop Vdd mbed p11 -> prop P0 (mosi) mbed p12 -> prop P1 (miso) mbed p13 -> prop P2 (sclk)