Trying to use I2C on a PICAXE28X1 Firmware level A.6. Its simply not working, why?

[der_fisherman]

Hi,

I am using a 28x1 PICAXE firmware level A.6, on a 28 Pin Project Board.

I am an almost total beginner with any sort of PICs though I was in the computer industry for almost 40 years. I was in hardware, but learnt assembler programming as well as BASIC (many years ago! For my O.U. courses). I programmed a lot in GWBASIC over the last 30 years (but not lately!), but for myself only.

My frustration is mostly with myself with regard to the I2C problems I am having.....

I want to control/use both a DS1307 RTC and an EEPROM 24C32. Both are mounted on the same tiny PCB. With a scope I can see the output LED signal of the RTC chip on the pin marked as SQ. This leads me to
believe that the RTC chip is working as designed.

I have added the necessary pullup resistors onto that tiny PCB, pulling sda and scl up to Vcc, using 4K7 resistors.

I read in the PICAXE Manual 1, it mentions for my chip that pins 13 and 14 (on the C output bank) are SCL and SDA respectively. But even writing to the RTC continuously in a tight loop, I was unable to
see any signals on those pins at all. I used a LED and a series resistor (as shown on PICAXE Manual 1 page 7), later with with an Oscilloscope. I am pretty sure that the PICAXE 28X1 is NOT outputting
anything on either of these two pins when using hi2cxxx commands.

I cannot find in any PICAXE documentation to do with I2C , a full 100% confirmation that these are the correct pins (14 & 15) to use (or not!).I suspect that they are.....and Rev-Ed staff kindly said they were as well. I trust his knowledge implicitly.

I am able to use the "C" outputs in other ways with no problems, setting them to outputs, outputting simple signals, all of which could be seen on the 'Scope screen. Just to be sure, I replaced the PICAXE chip twice with identical chips, no difference. Still no I2C activity to be seen.

The programs I wrote were accepted by the PICAXE Editor syntax checker, so the commands were correct for a 28X1 chip. Version 5.5.6. Not the Beta version.

I could also not get the pulsout command to work on the "C" outputs either.....though I only checked that with a LED, not with the 'Scope.

I also find that the documentation to be a bit strange (outdated?) in some puzzling (for me at least!) respects. If I look at I2C commands in the Manual part 2, I find newer commands such as Hi2cin,
i2cout and Hi2csetup with a partially good explanation, but also mentioning that "Use of I2C parts are in more detail in the separate I2C Tutorial" datasheet.

But in that sheet named "I2C Tutorial", no mention is made of any of the HI2Cxxxx list of commands, only ones like readi2c, i2cslave, writei2c. All of which are mentioned in PICAXE Manual 2 as being
"command is deprecated".......which I take as meaning it still works, but is not usually used anymore.......why is the "I2C Tutorial" datasheet not updated to reflect other, more update changes and commands?

Also, it would be helpful if the correct interfacing technique required for I2C usage was also documented in that datasheet. I just connected the two output pins to my PCB, where the pullup resistors are mounted. I connected the pins 14 & 15 to the RTC and EEPROM PCB, pins SDA, SCL and ground.

My personal take (as a beginner with PICs of any sort), is that the data sheet "I2C Tutorial", should be updated and have added the full hardware information for which pins are to be used for each and every PICAXE Chip......Short demo programs shown need to be commented with much more detail and newer commands also to be included. Leaving of course the older commands for those still using older chips of course.

I would also like to see in all manuals, that it is explicitly mentioned for which chips, which commands are used as some of the explanations near the Pin out diagrams are open to misunderstanding I feel.....

Please do not be upset with me, some of what I write here is probably wrong, for which I apologize, but as a beginner, floundering around for more than 4 days trying to make I2C do something! It is very frustrating.

I have to say that I still find that the PICAXE system to be one of the most exciting developments around that I have ever seen in my life, even though I am a relative latecomer to such technology. I am sure that many schools will be able to produce far more computer literate pupils than before and not forgetting the governments new trend on "coding" for schools, your products will be in even more demand in the UK and Ireland.

Well done is all I can say.

Many thanks in advance for any help given. I will be most grateful. I am sure its my lack of knowledge that gives me the problem(s).

Andy

Added later on Wednesday 12th March 08:00 MEZ/CET:-

I neglected to mention that I am using the PICAXE 28 Project PCB, with the 10K pullups still in place, do I need to remove this resistor pack, even though I can switch the inputs to outputs and make them high and low at will and see that on a scope screen.?

 

[lbenson]

Manual 1, page 34 says that SLC is pin 14 and SDA is pin 15 for the 28X1, not 13 and 14.

You say you added resistors to the module--are you sure it didn't already have resistors--all the ones I have bought (about a dozen) did.

Are you sure you didn't solder resistors to the addressing pads? What address are you using? Which modules?

Provide sharp photos, both sides, of your module and your picaxe wiring.

 

[hippy]

Probably the best way to get I2C working is to concentrate on doing just one thing first. Writing a single byte to a single I2C EEPROM and being able to read that back would be a good place to start. If that doesn't work then resolving why not will probably have everything else working as well.

 

[Technical]

As pointed out above the sda / scl pins are shown on the pinout diagram of the chip (legs 14 and 15).
Also if using the AXE020 project board you need to take into account that all the portC pins have a 10k pull down resistor fitted by default.

 

[bryanl]

I think the manuals are a bit confusing sometimes and successive updating hasn't helped much IMHO. The 'h...' commands usually indicate a more advanced than previous chip capability that provides improved hardware support for functions like I2C.

My Tiny RTC chip had the pullups on it. There are some good ideas about proper pin connections and boards, too.

The initilization uses -- hi2csetup i2cmaster, %11010000, i2cslow_8, i2cbyte
The binary number is for the clock. You'll need to get the right slave address for the EEPROM - there's a table of common device addresses in manual 2 page 79.
If I understand correctly, you need to re-issue a hi2csetup every time you want to access a different device on the I2C bus.

and a clock read starting at byte ten of the clock SRAM -- hi2cin 10, (tpos, spos, apos, zpos, dpos, mpos, wpos, tz)

One decent rundown is at http://www.bristolwatch.com/picaxe/serial_i2c_demo.htm - he's using an 18M2

The problem with using a scope to look for I2C signals is likely to be in the signal and response nature of the protocol. While going after that protocol and doing it by hand can be an educational exercise but not one, I think, for the intended PICAXE audience.

Also keep in mind that call PICAXE BASIC is kind of a stretch. It might promote some warm fuzzies and have a few similarities in syntax but it really isn't BASIC IMHO. When I think about the PICAXE programming paradigm, terms like lack of orthogonality and fractured underlying model start swirling around the brain.

If you get it right, it just works and is a lot of fun. If you miss something, it's another story.

 

[inglewoodpete]

I'd suggest two things:

1. Post your minimalised code that you are using to test your hardware in this thread
2. Remove both slave chips from the board and try the i2c code wile monitoring the scl and sda pins. The PICAXE will misbehave when you do this because there is no slave to respond. However, you should see some toggling of the pins (Legs 14 and 15).

The 28x1 does work and can run reliably - I have a system that uses the 28x1 with 8 slaves on the i2c bus.

Finally, it is possible that you have a damaged chip but, from my experience, this is extremely rare.

 

[der_fisherman]

Manual 1, page 34 says that SLC is pin 14 and SDA is pin 15 for the 28X1, not 13 and 14.

You say you added resistors to the module--are you sure it didn't already have resistors--all the ones I have bought (about a dozen) did.

Are you sure you didn't solder resistors to the addressing pads? What address are you using? Which modules?

Provide sharp photos, both sides, of your module and your picaxe wiring.

Firstly many thanks for your valued time in helping me. I will try and answer all your good points that you made.
I was wrong when I quoted Pins 13 and 14, I meant 14 and 15 as you said.
I have just had a look at the unit, there appear to be no resistors already on the PCB, but I will "pop" one end off each resistor and measure again to see if I have made a mistake. I will update later on that (good!) point of yours.
Thanks for mentioning it, but I know which are the addressing pads for the EEPROM, I have not used them yet. But anyone else with a similar problem would be wise to check, so thanks for that point as well.
I was using the address D0h or 11010000.
The module I bought on ebay Germany, it appears to be a fairly standard one sold by many here with either white or blue PCB surface/coating...

I wish I had a camera that could make good fotos up close, but I don't. I will try with my scanner! If it works, I will post fotos later, OK?

Many thanks for both your interest and help.

Regards

Andy

 

[der_fisherman]

Probably the best way to get I2C working is to concentrate on doing just one thing first. Writing a single byte to a single I2C EEPROM and being able to read that back would be a good place to start. If that doesn't work then resolving why not will probably have everything else working as well.

Hi Hippy,
you are a good Guy to have on my side, thanks.
I have already done this to no discernible effect according to my O'Scope.
As I am using the PICAXE28 Project PCB, there are "Pull-downs" on the CPort pins, do I need to remove this resistor pack (If yes, I would replace it with an inline socket to allow easy re-use if ever needed). It would appear that I have a 10K pulldown on all C port pins and a 4K7 Pullup each on pins 14 and 15......
Is that right?
regards and thanks for your help and interest.
Andy

 

[der_fisherman]

As pointed out above the sda / scl pins are shown on the pinout diagram of the chip (legs 14 and 15).
Also if using the AXE020 project board you need to take into account that all the portC pins have a 10k pull down resistor fitted by default.

Thanks for your input. Do you mean that I need to remove this resistor pack?
As I said in answering another email (before I got to yours) I would eventually replace it with a socket for easy replacement.
Maybe PICAXE should do this as a matter of course......only a few cents in cost.....
regards and many thanks.
Andy

 

[der_fisherman]

I think the manuals are a bit confusing sometimes and successive updating hasn't helped much IMHO. The 'h...' commands usually indicate a more advanced than previous chip capability that provides improved hardware support for functions like I2C.

My Tiny RTC chip had the pullups on it. There are some good ideas about proper pin connections and boards, too.

The initilization uses -- hi2csetup i2cmaster, %11010000, i2cslow_8, i2cbyte
The binary number is for the clock. You'll need to get the right slave address for the EEPROM - there's a table of common device addresses in manual 2 page 79.
If I understand correctly, you need to re-issue a hi2csetup every time you want to access a different device on the I2C bus.

and a clock read starting at byte ten of the clock SRAM -- hi2cin 10, (tpos, spos, apos, zpos, dpos, mpos, wpos, tz)

One decent rundown is at http://www.bristolwatch.com/picaxe/serial_i2c_demo.htm - he's using an 18M2

The problem with using a scope to look for I2C signals is likely to be in the signal and response nature of the protocol. While going after that protocol and doing it by hand can be an educational exercise but not one, I think, for the intended PICAXE audience.

Also keep in mind that call PICAXE BASIC is kind of a stretch. It might promote some warm fuzzies and have a few similarities in syntax but it really isn't BASIC IMHO. When I think about the PICAXE programming paradigm, terms like lack of orthogonality and fractured underlying model start swirling around the brain.

If you get it right, it just works and is a lot of fun. If you miss something, it's another story.

Firstly many thanks for your help and interest.
I will be checking the pullups are not doubled up later today.
The link you provided was of particular interest to me and once I have the communication working, I will be going back there.
I am trying to find out if I need to remove the 10K pulldowns to get I2C working properly.....can you help there?
I agree about BASIC here not being BASIC, its a completely new language, but that is fine, I will apply myself to learn it properly.......It fires me up, just reading about it on this great forum, but it is more difficult than I thought before I bought the Project PCB.
Hopefully it keeps the old brain cells ticking over!!
Many thanks again and regards from
Andy

 

[der_fisherman]

I2C Problems on a 28X1

I'd suggest two things:

1. Post your minimalised code that you are using to test your hardware in this thread
2. Remove both slave chips from the board and try the i2c code wile monitoring the scl and sda pins. The PICAXE will misbehave when you do this because there is no slave to respond. However, you should see some toggling of the pins (Legs 14 and 15).

The 28x1 does work and can run reliably - I have a system that uses the 28x1 with 8 slaves on the i2c bus.

Finally, it is possible that you have a damaged chip but, from my experience, this is extremely rare.

Removing the slave chips is not possible due to it being SMD and has a guarantee that I do not want to damage, even though it was very cheap.

I am trying to find out if I need to remove the 10K resistor pack, working as Pulldowns on the C Port pins on the Project PCB before doing anything more.....

The PICAXE is not "misbehaving".

I have replaced the chip twice just to be certain, I do not expect any to be damaged as they were all identical in NOT working as expected (by me!).

I made a loop with an Hi2cout command for the RTC, no signal changes were seen on pins 14 & 15 with the Scope, though I can set all the pins as outputs and change them to high and low and see the changes on the scope screen using other commands.

Many thanks for your help and interest.

Regards
Andy

 

[der_fisherman]

Pictures of my DS1307 RTC PCB as requested.



The first is of the top, the second is showing the pins and the 4K7 resistors for SCL and SDA.
I hope the pictures are usable! They were done using my scanner, not a camera......
Andy

 

[hippy]

I am trying to find out if I need to remove the 10K resistor pack, working as Pulldowns on the C Port pins on the Project PCB before doing anything more.....

That may well be the case, or at least disconnect the pack connections going to the I2C bus lines.

 

[der_fisherman]

Regarding the 10KOhm resistor pack on the PICAXE28 Project PCB C Port I/O

That may well be the case, or at least disconnect the pack connections going to the I2C bus lines.

I may do that this afternoon, although I would like it if someone else here was certain 100% that this is my problem. I' m not certain, and you appear not to be either.....that is not intended to be rude by the way....

Many thanks for your input and do keep watching (and helping!) and I will probably take your advice later today....I am just hoping that a similar "voice" will also chime in....

No mention is made of this need in the Project Board notes/datasheet either....if true, that should be changed.....I will personally do my best to get that done. I feel that an inline socket would be the better alternative for all concerned rather than the resistor pack soldered in.

Regards

Andy

 

[westaust55]

Keep in mind that the two pins when used for i2c comms are open collector so they can be pulled low by the PICAXE but not driven high.
Combined with the pull down resistor alone you would see no signal. Adding 4.7 kOhm pull-up resistors with the 10kOhm pull-down still in place then signal will only reach about 1.5 volts at idle.

 

[hippy]

I may do that this afternoon, although I would like it if someone else here was certain 100% that this is my problem. I' m not certain, and you appear not to be either.....that is not intended to be rude by the way....

A functional I2C bus would not normally have pull-downs so a non-working I2C bus with pull-downs may be explained by the presence of pull-downs and removing those pull-downs may turn it into a working I2C bus.

I recall there is past evidence that pull-down resistors can adversely affect the I2C bus but there is no absolute certainty that this is the problem or only problem with what you currently have.

No mention is made of this need in the Project Board notes/datasheet either....if true, that should be changed.....I will personally do my best to get that done. I feel that an inline socket would be the better alternative for all concerned rather than the resistor pack soldered in.

The 28-pin project board was not designed to be used with I2C, it was designed for accepting 8 digital inputs on the port C port. Having a soldered in SIL resistor array is appropriate for such use but does mean it may require modification for other uses.

How any board should be designed or documented to cater for being used beyond its intended use will always be a matter for debate but we do appreciate feedback on such issues.

 

[Goeytex]

... I would like it if someone else here was certain 100% that this is my problem. I' m not certain, and you appear not to be either.....that is not intended to be rude by the way....

The pull downs on pins 15/14 need to be removed ... period. Nowhere in the I2C specification are pull downs, specified, allowed or suggested.... only a pullup. While they may not be solely (%100) responsible for your problem, they will cause the 12C signal to be degraded. Remove them. If you still have trouble, then we can go from there.

Things are not always black or white where only 1 thing causes the problem. Many times there are multiple causes or an accumulation of errors that cause a failure.

How can anyone be 100% certain that the resistors are causing your problem without removing the resistors ?

We can however be 100% certain that the pull down resistors are not part of the I2C specification and should be removed, regardless of any other issues. -

 

[Technical]

You could consider this board instead, which is designed for 28/40 pin chips and is intended to directly support i2c (there is on-board provision for pull up resistors and an EEPROM)

http://www.picaxe.com/Hardware/Project-Boards/PICAXE-2840-Proto-Board/

 

[der_fisherman]

Keep in mind that the two pins when used for i2c comms are open collector so they can be pulled low by the PICAXE but not driven high.
Combined with the pull down resistor alone you would see no signal. Adding 4.7 kOhm pull-up resistors with the 10kOhm pull-down still in place then signal will only reach about 1.5 volts at idle.

I understand, many thanks. I will remove the resistor pack later toay in a friend's workshop, where all the right tools are available....
I will post once I have made the tests again.....
Many thanks
Andy

 

[der_fisherman]

28X Project board possible mods

A functional I2C bus would not normally have pull-downs so a non-working I2C bus with pull-downs may be explained by the presence of pull-downs and removing those pull-downs may turn it into a working I2C bus.

I recall there is past evidence that pull-down resistors can adversely affect the I2C bus but there is no absolute certainty that this is the problem or only problem with what you currently have.

The 28-pin project board was not designed to be used with I2C, it was designed for accepting 8 digital inputs on the port C port. Having a soldered in SIL resistor array is appropriate for such use but does mean it may require modification for other uses.

How any board should be designed or documented to cater for being used beyond its intended use will always be a matter for debate but we do appreciate feedback on such issues.

I agree with you, but I will definitely modify mine to an inline socket where I can the "Pulldown" only the signals I wish and when....that is surely for similar reasons that the other chips are all beautifully socketed - just in case!! The explanation of the Pullup and the pulldown seems to be right in my mind, I only wonder why I was so slow to think of it myself!!

The PCB is otherwise a perfect way to start with any 28 pin chip. AS LONG AS YOU KNOW!

Are other Project PCBs also maybe looking at a possibly similar problem?

The PICAXE parts in the UK are still fantastic value for their prices and even if it cost a little bit more for the mod to be added to later versions, I feel that would be a good/useful change to make personally. Of course, only the real "longterm Dyed in the wool PICAXERS" can really answer this for certain.....which I am a LONG way from being at this time!!

Furthermore, at least the Datasheet needs to be modified to reflect this (possible!) problem with I2C signals (assuming that it is correct so, I have not actually tested it as of now!) to alert any other user of that product as to why I2C does not work on that PCB as supplied.....it has cost me 6 days of testing and blood, sweat & tears.....(again assuming that it is the problem for the moment, but it "rings" of truth!!)

I will try and give an update within the next 24 hours.

Many thanks Hippy (and everyone else as well!) for your time and trouble (that I seem to have caused you all!!)

Best regards

Andy

 

[der_fisherman]

28X1 Project PCB and breadboard cables

You could consider this board instead, which is designed for 28/40 pin chips and is intended to directly support i2c (there is on-board provision for pull up resistors and an EEPROM)

http://www.picaxe.com/Hardware/Project-Boards/PICAXE-2840-Proto-Board/

Thats a nice PCB, thanks for reminding me about it.

With the right pins (see below in picture), it could be made to plug into a breadboard when required. I am adding a picture of the pins I have found on ebay, very cheap, here in Germany, with a 0.1" raster, they fit really well on my RTC PCB and any normal breadboard.

The reason I bought the project PCB I did was that it was on ebay with extra spare chips (in all 3 x 28X1 chips) and the flat cables, CD and the USB Download cable. I bid €35 and got it for €11,75 including postage (under 10 pounds Sterling!), a steal!! It had never ever been used and was missing only the battery box. The latest files on the CD are from 2010, so I guess it is 3 - 4 years old.....the red plastic protection was still stuck in the holes that need to be kept solder free underneath!!

I also managed to buy some other simple cables as well to assist me further with my experimenting, also shown in the picture! Some cables going from Breadboard to Breadboard and some going from project board pin to breadboard....the last one being a socket on one end and a pin on the other.....all very cheap from ebay.....

Best regards to all

Andy

 

[lbenson]

I have the same RTC board, designed by "Waiman" and it does have the pullup resistors onboard. Note the label "472", which indicates 4.7K ohms. As others have said, any pulldowns should be removed, and additional pullups should be removed.

As with IP, I have had I2C working on a 28X1--with separate DS1307 clock chip on a breadboard.

 

[der_fisherman]

I2C Problems on a 28X1 Now fixed and working!!

I removed the "extra" 4K7 pullup resistors and the 10 K resistor pack on the C Port of the 28X1 project PCB.

It now works!!

I can see proper SCL & SDA signals with my scope when doing a fast loop. I am ecstatic!!!

After 5 days in all of head scratching on my own, I can now tell the RTC/EEPROM seller on ebay that everything is OK......and give him a good recommendation.

Many, many thanks to all of you Guys here on the PICAXE Forum, you helped me fix it in less than 24 hours!!! Without you I would still be scratching my head (and still have had FAR too many resistors installed!)

I knew before that this was a great place to visit, but I did not realise just HOW great!!

See you all again soon.

Regards

Andy

 

[lbenson]

Congratulations. Note that many of the inexpensive DS1307 RTC modules like yours (and all the ones which I have bought) are not really very accurate, apparently because of lack of tight specs on the auxiliary parts used. The DS3231 modules for a couple of dollars more are as accurate as you would want.

 

[der_fisherman]

Congratulations. Note that many of the inexpensive DS1307 RTC modules like yours (and all the ones which I have bought) are not really very accurate, apparently because of lack of tight specs on the auxiliary parts used. The DS3231 modules for a couple of dollars more are as accurate as you would want.

You could be right, but it runs too fast I will place a 1pF trimmer over it and see what that does for me.....Just for fun!! Eventually, I may be able to change that for a fixed value.
Eventually, I may add a Radio Atomic clock receiver, they don't cost much and stop using the RTC completely....
Regards
Andy

 

[der_fisherman]

Keep in mind that the two pins when used for i2c comms are open collector so they can be pulled low by the PICAXE but not driven high.
Combined with the pull down resistor alone you would see no signal. Adding 4.7 kOhm pull-up resistors with the 10kOhm pull-down still in place then signal will only reach about 1.5 volts at idle.

If I set them to outputs, I can drive them high and low at will. That was part of my testing that I tried out before removing the 10K resistors....the resistors were there to pull down to 0 volts, so if what you said was true, nothing could cause a high on those port pins, ever.....Of course you can set them how you wish....

Thanks for trying to help, the thought was there....

Regards

Andy

 

[lbenson]

>if what you said was true, nothing could cause a high on those port pins, ever

That's not what he said, or at least, not what he meant within the context of I2C. Yes, setting a picaxe pin high with "high C.0" will overcome a 10K pulldown, but that's not the way I2C works. I2C is pulled high with a 4K7 resistor, unless the pin pulls the line low. You had, apparently, 2 4K7 pullups and a 10K pulldown--out of spec, and so observations might vary depending on what I2C devices were connected. Your circumstance would seem at the very least to be undefined.

 

[der_fisherman]

You could be right, but it runs too fast I will place a 1pF trimmer over it and see what that does for me.....Just for fun!! Eventually, I may be able to change that for a fixed value.
Eventually, I may add a Radio Atomic clock receiver, they don't cost much and stop using the RTC completely....
Regards
Andy

It runs 2 minutes too slow per day, I will correct it daily in software.....cheap Chinese chips, maybe with a crystal with too high capacitance....but who cares for that price?
Regards
Andy

 

[westaust55]

Daily time adjustments may be acceptable if your PICAXE and RTC are operating 24 hours per day.
If only operating part of the time / infrequently or there is a power cut/failure at the intended adjustment time that would be a problem knowing whether the adjustment has or has not been made.

It may be worth sourcing a crystal with the correct pF capacitance loading as specified in the DS1307 datasheet.
There are some RTCs with the crystal inbuilt to the RTC chiup. Some are based on the same "core" as the DS1307 hand have the same operating tolerances while others such as the DS3231/3232 parts have a greater overall accurancy but will cost slightly more.

 

[der_fisherman]

Keeping time!!!!

Daily time adjustments may be acceptable if your PICAXE and RTC are operating 24 hours per day.
If only operating part of the time / infrequently or there is a power cut/failure at the intended adjustment time that would be a problem knowing whether the adjustment has or has not been made.

It may be worth sourcing a crystal with the correct pF capacitance loading as specified in the DS1307 datasheet.
There are some RTCs with the crystal inbuilt to the RTC chiup. Some are based on the same "core" as the DS1307 hand have the same operating tolerances while others such as the DS3231/3232 parts have a greater overall accurancy but will cost slightly more.

Many thanks for your comments, they fully agree with my own personal knowledge.

Once testing is completed, further units will be made with an Atom clock receiver, I believe I mentioned that in a previous post. It costs around $15 and is also I2C capable....

Usually digital clocks run too fast (in my experience) and need a low value trimmer cap to slow them down, usually its already in place for that purpose. A good source of accurate time and a week or two of tweaking occasionally, gets the clock running so that just DST changes are often enough to keep the clock accurate to within a few seconds.....

I have a Braun alarm, that when a DST change comes, it is less than 10 seconds wrong.....far more accurate than most people ever need, but I enjoy setting up such things as well as possible....

Also, in keeping with many similar units sold, the RTC pcb has a rechargeable battery, that is calculated to be able to keep the clock running for about a year without power.

I believe that its unlikely that power failures will last that long!!!

Careful programming will allow the time lapse between the power loss and power return to be calculated and the requisite correction to be applied.

Thanks for your time and interest, I hope to read further comments from you and people like yourself, me being a "Newbie" in the PICAXE area...have a great day....

Regards

Andy