PICAXE Manual Section 1 - TechnoPujades - Free

www.picaxe.co.ukSection 1 36GETTING STARTEDUSB Download CircuitThe USB download circuit is identical for all PICAXE chips. It consists of 3 wiresfrom the PICAXE chip to the AXE027 USB cable. One wire sends data from thecomputer to the serial input of the PICAXE, one wire transmits data from theserial output of the PICAXE to the computer, and the third wire provides acommon ground.Note this circuit can also be used for the AXE026 serial cable. Therefore the samecircuit can be used with either USB or serial cable.The minimum download circuit is shown here.abcAbove viewxxcxxxab10k22kserial outserial in0VPICAXENote that the two resistors are not a potential divider. The 22k resistor works withthe internal microcontroller diodes to clamp the serial voltage to the PICAXEsupply voltage and to limit the download current to an acceptable limit. The 10kresistor stops the serial input ‘floating’ whilst the download cable is notconnected. This is essential for reliable operation.The two download resistors must be included on every PICAXE circuit (i.e. notbuilt into the cable). The serial input must never be left unconnected. If it is leftunconnected the serial input will ‘float’ high or low and will cause unreliableoperation, as the PICAXE chip will receive spurious floating signals which it mayinterpret as a new download attempt.revolution(c) Revolution Education Ltd. Email: info@rev-ed.co.uk Web: www.rev-ed.co.ukVersion 6.9 07/2009All rights reserved.36