8
revolution
Revolution Education Ltd. Web: www.picaxe.co.uk
Version 1.3 04/11
AXE401.PMD
AXE401 PICAXE-28X2 Shield Base
4.0 PICAXE USB download cable
The AXE027 PICAXE USB cable is recommended. This is widely available from
various PICAXE distributors around the world. It works reliably with Windows, Mac
and Linux. You may alternately also use universal USB-to-serial converter cables
(make sure they have a Prolific or FTDI chipset) with a home made cable.
The AXE027 contains an internal FTDI USB-to-serial conversion circuit,
specifically optimised for the PICAXE system. This FTDI chip is the same
chip that is often found on other shield bases (e.g. the Arduino
Duemilanove). However building the chip into the cable instead of the
shield base has several advantages:
1) The cost of each shield decreases, as you only purchase the USB chip
once when you purchase the cable (rather than buying a USB chip on
every shield base).
2) The FTDI chip is only available in a very small surface mount format,
so it would make a self assembly PICAXE shield base almost
impossible.
3) A single download cable can be used for all your different PICAXE
projects, even those not built upon shield bases.
Therefore the initial cost of the ‘intelligent’ AXE027 download cable is slightly more
expensive than a non-intelligent ‘printer’ style USB cable, but has the advantage that
it can be used across all your PICAXE projects, and will also work out more
economical in the long run if you purchase more than one shield base or project
board.
4.1 Why the download cable jumper links H2 and H3?
The PICAXE-28X2 system uses completely separate pins of the PICAXE chip for new
program downloads. Therefore the digital hardware serial port pins (S.0 and S.1)
have no effect on new program downloads. Data within the program can also be
transmitted directly back to the computer (without using S.0/S.1) via the download
cable with the debug, sertxd and serrxd BASIC commands.
However on occasions for some projects it might be desired to have the S.0 and S.1
i/o pins connected to the download cable. This can be achieved via the jumpers H2
and H3.
AXE401 PICAXE Shield Base - Download Circuit
x
x
x
x
x
H2
GND
RXD
S.0 (C.7)
H3
TXD
S.1 (C.6)
R2
10k
R3
22k
CON2
H3
Default positions of the 4 jumper links
3V3
H1
5V
H4
H2
H1 - 5V - Top
H2 - RXD - Bottom
H3 - TXD - Bottom
H4 - LED - On
LED