Although PICAXE microcontrollers are now well established and popular in numerous
electronic projects, due in no small part to SILICON CHIP’s enthusiasm, many users
know only of the entry level 08M, versatile 18X or powerful 28X.
The three "M" PICAXES are very similar in pinouts and architecture, meaning little change in code as you move up the chain (in fact, the 08M is pin-for-pin for the top eight of the 14M). The main difference is all those beautiful extra inputs and output channels!
However, the recent arrival of a 20-pin PICAXE now takes the
family to an awesome 14 members, although four earlier offerings are now
discontinued and two "X2" fire breathers have yet to be released. This new
PICAXE-20M (based upon a MicroChip PIC16F677) is really just a stretched 08M, as
it offers similar memory and follows the same commands as the ever popular 08M
and more recent 14M.
Thankfully, its 10-a-side DIP packaging enables easier
identification in the sea of chips lurking in many IC parts drawers, since its
20 pins make it noticeably longer than common 14,16 or even 18-pin DIP logic
The so-called 20M is mainly intended to meet the demand for
further input and output (I/Os) channels than the four offered by the smaller
08M, or 5-6 of the 14M.
Its provision of eight I/Os, arranged with inputs (0-7) on one
side and outputs (0-7) on the other, looks to have strong appeal for projects
where extra chips (such as Shift Registers) and wiring would otherwise be
Circuit size will naturally be reduced with just a single IC,
yet greater flexibility will result, thanks of course to the PICAXE programmable
All three "M" chips are especially well-suited for hobbyists
and educational users, allowing enhanced design for just a few dollars more,
when the need for extra I/O channels arises.
Pleasingly, the larger 14 and 20 "M" offerings retain the same
programming and supply connections as the classic 08M, although only the 08M
allows pins to be set either as Inputs or Outputs.