M2 vs M2+ differences

Andy2No

Member
I've looked for this a few times, but I don't see anything that says what the differences are between the M2+ versions and the M2 versions, e.g. in what ways do 08M2 and 08M2+ or 18M2 and 18M2+ differ?

Unless I'm missing something, the M2+ versions don't seem to have been announced in the New Product Releases section, and the latest manuals (or at least the ones I downloaded quite recently) only go up to the M2 versions.
 

mrburnette

Senior Member
Andy,

Just returned from putting 300 miles on my butt for my Mother-In-Law's birthday... But... to answer your question, here is the 18M/M2+ differences:
http://www.picaxe.com/docs/picaxem2.pdf
See the section titled M2 Part Comparison

I have seen the 08M/M2+ somewhere... I'm trying to find it... but the data sheet for the current part is here:
http://ww1.microchip.com/downloads/en/DeviceDoc/41441B.pdf

Later....
See Post #7. It appears that when RevEd says 08M2 they mean the chip with the label 08M2+ ...
08M2+microchip


- Ray
 
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Andy2No

Member
Thanks, Ray.

I'm glad you survived your trip.

I'd actually read that document too, but my memory is rebelling against me trying to stuff too much into it in a short space of time. It looks like the 18M2+ was the first M2+ then, and the documentation hasn't caught up yet. It seems strange that they didn't announce them in the Releases section - unless they're there and I just can't see them.

Most of the 18M2+ vs 18M2 differences look like changes in the firmware, apart from the Table data part. Is that in EEPROM that the 18M2 doesn't physically have?

It's mostly the 18M2/18M2+ differences I'm interested in at the moment, because I have both. I have 08M and 08M2+ but not 08M2.

EDIT: Okay, I see that table data refers to data stored in the program memory space. So does the 18M2+ have more Flash, or does using table data just reduce the amount of program space available?
 

mrburnette

Senior Member
Andy,

Table data always reduces the program memory... from my understanding.UPDATE... this is incorrect see Technical's post below!
From the Online Command References for Table ... Description:
Specify values to be loaded to the internal lookup table when the program is downloaded.​

M2 parts have 512 locations (0-511). Other parts have 256 (0-255).

This is not an instruction, but a method of pre-loading the microcontroller's program memory lookup table. The data can then be read via the readtable command (the data is fixed, cannot be altered apart from at program download). The tablecopy command may be used to copy the table data to RAM in sections.

18M2 Firmware

Please note the 'table' command is only supported for 18M2 firmware D.x (PICAXE chips labelled 18M2+) and is not available for use with 18M2 firmware 2.x (PICAXE chips labelled 18M2).
It would appear that RevEd is using the "+" to indicate major firmware upgrade on the same silicon.

I think this explains what you are after for other differences: docs/picaxem2.pdf
Memory Capacity
The M2 parts now have up to 2048 bytes of program memory, which is 8x larger than the older M parts.
They also contain 256 bytes of data memory (read/write/eeprom commands).
On the 14M2, 20M2 and 18M2+ the program memory and data memory are completely separate (2048 + 256).
Due to more limited silicon resources on the 08M2/(older)18M2 the upper 256 bytes are shared between program
and data (2048 in total). Therefore with programs that are under 1792 bytes long all 256 bytes of data memory are
available. Very long programs (over 1792 bytes) start to reduce the amount of data memory available.
See: eeprom,
 
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Technical

Technical Support
Staff member
The + is just a convenient identification marker, not a totally new PICAXE chip style. So the chips marked 18M2 and 18M2+ are regarded by the manuals and software as the same chip (just different revisions).

www.picaxe.com/docs/picaxe18m2.pdf explains the difference - so the 18M2+ is now a direct equivalent of the newer 14M2 and 20M2 (even though they don't have a + marker).

table reduces the downloadable program length by 256 bytes on X2 parts only. On M2 parts it does NOT reduce the 2048 limit - it is separate area of memory.
 

Andy2No

Member
Thanks, Ray and Technical,

The 18M2+ is the only M2+ part that www.picaxe.com/docs/picaxe18m2.pdf mentions, as far as I can see, which is a little confusing.

So can you confiirm that the M2 and M2+ parts are the same physical chips, Technical, just with different firmware?

So I take it Table data is stored in Flash? If so, is it Flash that was just unused on the 18M2?
 

mrburnette

Senior Member
@Technical
I suspect that more than a few longtime PICAXE hobbyists have a few flavors of various PICAXE models in their parts drawers. For example, I have both 08M and 08M2+ as well as 18M2 and 18M2+ with a tube of 20X2s in the corner. While I can deal with firmware, the changes in silicon are most important.

So, it surely would be nice to have a complete chronology of PICAXE in one place, current and past data sheet links as well as the various firmware that was shipped. The key takeaway here is "in one place."

I realize that such info has little value beyond advanced experimenters, but it surely would be nice to have... maybe a link off this page:
http://www.picaxe.com/What-is-PICAXE/PICAXE-Chip-Sizes/
 

Andy2No

Member
Since the 18M2+ has twice the RAM, must be different silicon.
So it does. Which makes me wonder, is the 18M2+ based on a PIC that's available as just a PIC, like the earlier PICAXEs, or is the underlying silicon only available as a PICAXE?

I know the documentation says they were made specially for Rev Ed, but I wasn't sure if that meant they're a standard chip made with the firmware burned on already, or if they really are a unique chip - in which case, does the PIC 16(L)F1847 data sheet cover the 18M2+ properly?

As Ray said, a page giving the complete technical details of all PICAXEs, going back to the original versions, would be good. I'm sure there are still plenty of the older ones out there.
 

mrburnette

Senior Member
... there was a time in the not so distance past when getting confirmation on PIC data sheet "matching" was nearly impossible. Regards to RevEd for opening the process and posting uC data sheets and in being more open to assisting in this area.

I know the documentation says they were made specially for Rev Ed, but I wasn't sure if that meant they're a standard chip made with the firmware burned on already, or if they really are a unique chip
@Andy2No...
Interesting ... I cannot remember seeing a definitive, official answer. I have seen many "suggestions" however. But I sometimes notice threads where Technical or Hippy have made a product statement. In the past, I have gone to their profiles and read through their posts in an effort to gleam such insight... but not recently and I am overdue.

- Ray
 

Technical

Technical Support
Staff member
All past and current chips are already listed here. The base microcontroller technical datasheet are clearly linked.
http://www.picaxe.com/What-is-PICAXE/PICAXE-Chip-Labels/

http://www.picaxe.com/What-is-PICAXE/Superseded-Parts/

All parts, past and present, are in the manual. There are no 'previous' PICAXE datasheets, the manual still covers them all.

Firmware revisions of current parts, plus their various datasheets are on their individual product pages, e.g.
http://www.picaxe.com/Hardware/PICAXE-Chips/PICAXE-18M2-microcontroller/
 

MartinM57

Moderator
I believe the emphasis is on "all in one place"

I don't think parametric searching is required, but a nice table, on one web page, kept up to date, with all PICAXEs (maybe every one, maybe at some arbitrary date) containing things like (and there's probably more, so chip in):
- name
- min/max Vcc
- max source/sink mA per pin
- max source/sink mA per pin
- no of pins
- no of I/Os (not "marketing counting" either!)
- no of PWMs (including no of independent)
- no of ADCs
- whether hardware SPI/I2C
- program memory
- EEprom memory
- Table memory (and whether it is taken from program memory)
- label on chip
- firmware versions/dates
- underlying PIC
- hyperlink to underlying PIC datasheet
...yes there will be a few footnotes as it's not always black'n'white for these sort of things.

I can't see any reasons why it wouldn't be extremely useful....

(oh...and a Buy Now link to techsupplies :))
 

Andy2No

Member
The base microcontroller technical datasheet are clearly linked.
http://www.picaxe.com/What-is-PICAXE/PICAXE-Chip-Labels/
That page indicates that the 18M2 and 18M2+ are both based on the PIC 16(L)F1847. That doesn't appear to explain the differences in the spec that Ray pointed out.

A table with all the details Martin suggested would be great. At the moment, choosing between PICAXEs, or getting a good overview of what's available, takes a lot of hunting around, and hours of looking through manuals. I started looking into PICAXEs again a few weeks ago, and I still only feel I have a fairly basic grasp of that information.

I appreciate that from a marketing point of view, only the current chips are of interest, but keeping the existing client base happy has to be worth doing too, so listing the whole range, back to the beginning, in one clear table, would benefit a lot of people.

I'd suggest adding a link to the pinout diagrams for each PICAXE in that table too. They're the main thing I keep going back to.
 

westaust55

Moderator

mrburnette

Senior Member
EDIT: ... Looks like a lots of the info is already on the hard disk after installing PE
\Program Files\Programming Editor\firmware.txt
View attachment firmware.pdf (Rhetorical: Am I the only idiot that did not know this was documented?)


@ RevED:

What I suggested and what I hear many of the members stating is a single (summary) document / web-page (we can print to PDF) covering all products supported by PE and notes to little 'strange' behaviors or enhancements. I suspect that within the PE source code comments is everything that is needed to create such a document and more... It would be a very useful extension to: http://www.picaxe.com/What-is-PICAXE/PICAXE-Chip-Sizes/

I believe that such a document would be most useful to the experimenter/hobbyist who works with more than one PICAXE model and maybe even schools that have mixed stock in chips... although perhaps instructors avoid such issues and remain consistent for the classes.

- Ray
 
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mjy58

Member
Have to agree with the majority on this thread, all in one place - really useful. Just tried to use 'table' command on 18M2 and got the dreaded table '(18m+ only)(Firmware >=vD.A)' error.

This thread was the first hit whilst trying to resolve why.

@Ray
Great post regarding firmware.txt. I had no idea that was there:).

But even that does not reveal the change in table command between the two variants.

Since getting the error and finding this thread, it is documented in Help > Quick syntax check and the online command reference.

One place - great idea.
 
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