ADS1298ECGFE-PDK some questions around the simple ECG implementation

Dear Sirs,

While evaluating ADS1298ECG-FE, I've found some strange behaviour, trying to measure MVdd. It seems that s/w doesn't actually measure data from ADS1298 (or I have an ideal ADS1298 with absolutely no noise :) ). Please take a look at attached pictures - these are channels' configs and the results.

Saved binary data for CH1, PGA=1:

As to ADS1298 datasheet such output is possible in case of Vin(AINP-AINN)>=VREF;

for CH=1; Vin=MVdd=0.5*(AVDD+AVSS)=0[in case AVDD=+2.5V;AVSS=-2.5V] (or  near 0)

I've checked VREF - it matches with settings - if I set it to 2.4 it becomes +2.4V ref. to AVSS.

UPDATED: After I've carefully read ADS1298 datasheet, I've found on p.21, document SBAS549E: (about MVdd) ...For channel 3 and for channel 4,(MVDDP-MVDDN) is DVDD/4..., but on p.28 of SBAU171 (ADS1298ECG manual): (about the same MVdd) ...the supply voltage for channel 3 will be DVdd/2. I've checked this - the original ADS1298 manual is correct - I've measured 0.815V (for DVdd=3.2V). What was wrong on attached pictures - I don't know... for ch.3,4 MVdd=DVdd/4. But the problem with all other channels still exists.

Another idea is that MMB0 reads "all ones" from ADS1298 due to some internal problems with sync or something else.

Everything else (temperature sensor, test signal, normal input signal) seem to be fine.

The binary output for MVdd seems to be calculated using this formula:

MVdd(n)=VREF/PGAn;

CH1, PGA=1, V=2.4V

CH2, PGA=2, V=1.2V

CH3, not calculated

CH4, PGA=3, V=0.8V [UPDATED: It's strange :) For PGA=3 it should be overflow. PGA should be 1 due to ADS1298 datasheet! If PGA is set to 1 for this channel, the measured value is near 0.8 and is DVdd/4 . And this is TRUE, I've checked this.]

CH5, PGA=4, V=0.6V

CH6, PGA=6, V=0.4V

CH7, PGA=8, V=0.3V

CH8,PGA=12,V=0.2V

May be it's my mistake, so please help to resolve this.

Thanks a lot!

Regards,

Ilia V. Davidov

As to these pics, there are ABSOLUTELY NO NOISE in MVdd channels!!! Vrms=0 :) Even shorted CH3 has some noise...

Hi Ilia,

We'll look over all of this and try to replicate what your are seeing - how are the other configuration registers set? 

Hi Tom,

Thanks for reply! :) Hope you'll help me.

To summarize everything I've read, done & discovered:

1)CH3, CH4 works fine with MVdd.

2)PGA _should_be 1 while measuring MVdd, as to ADS1298 datasheet.

3)See attached pictures (I've set all CHs to MVdd, PGA=1) and got that results:

...the settings was:

If you need some additional measurements - please inform me. Also it's possible to give you an access to RDP-session of the PC EVM is attached to - also please inform me if this will help.

Regards,

Ilia V. Davidov

Hi Ilia,

When using the ADS1298 in bipolar supply mode (W6 on pins 2-3 and W8 on pins 1-2) I see similar results to what you see when using the evaluation module.  If you go to single supply mode, the results are what you would expect to see.  We are looking into the cause/reasons for this now.

Hi Ilia,

OK - now that I have the correct board, let me try this again...sorry for the confusion here.

In single supply operation - JP24 on pins 1-2 and JP2 on pins 2-3, the scope analysis works correctly when the gains are set to 1 and the inputs are selected for MVDD reading.  In bipolar supply mode (JP24 on pins 2-3 and JP2 on pins 1-2), you will get the zeros in channels 1, 2, 5, 6, 7 and 8 if the VREFP is set for 2.4V (Configuration Register 3 under the Channel Registers Tab).  For the correct display, you need to change the VREFP to 4.0V.

Hi Tom,

Thanks a lot for your help. I've tried to do what you were talked about.The results are:

1)Are all these problems due to software bugs or is this a problem of ADS1298 chip itself (or, maybe, of it's datasheet)?

2)You say: "In bipolar supply mode... you will get the zeros in channels 1, 2, 5, 6, 7 and 8 if the VREFP is set for 2.4V...". What do you mean, talking about "zeroes"? Vrms? Or data? I have "all ones" in data, not zeroes... And Vrms are 0 for all these channels.

3)When I change the VREFP to 4.0V, I have MVDD for mentioned channels at levels about 2.5. Why so, why is it not [0.5*(AVDD+AVSS)]=approx.0 in bipolar mode?Or should I understand both AVDD and AVSS as |AVDD|+|AVSS| => [0.5*(|+2.5|+|-2.5|)]=0.5*5=2.5 (this looks like true, but WHY? :) )

As I understood the datasheet, MVDD doesn't depend upon a VREFP. In this case it's absolutely normally (in case if datasheet has mistake about the sign of AVDD and AVSS) that for MVDD=2.5 (>2.4) and VREFP=2.4V we have an overflow.

Hope you'll answer these questions - it may be usefull for others, who will evaluate the MVdd measuring feature. Waiting for reply!:)

Regards,

Ilia V. Davidov

Hi Tom,

Thanks a lot for comprehensive answer! If you are going to revise the datasheet, please also check p.28 of SBAU171, 5.6.1. about DVdd measurement. The supply voltage for ch. 3,4 will be DVdd/4, not /2. Also please compare Fig.24 on page 22 of SBAS459E to Fig.59 on page 65 of this manual: which input scematics diagram is correct? I think Fig.59 is correct, and both MuxP and MuxN should be connected to (+) poles of corresponding OPAMPS.

Also please explain more detailed the meaning of Common-Mode voltage.

For example:

• AVDD=2.5V, AVSS=-2.5V, DVDD=3.3V rel. to AGND
• ADS1298 is configured this way: CH1: PGA=1, Normal electrode mode, all other channels are powered off.
• I'm going to measure the voltage of simple AA battery (+1.5V). If this if enough to simply connect (+) to CH1P and (-) to CH1N? I've tried this, but the result was too noisy, with peaks at 50Hz (the outlet frequency). As it's a single-ended input I should connect CH1N to AGND if I'm going to measure only positive (unipolar) voltages and to reduce the noise. Is this correct?
• in case of real ECG, how is AGND of ADS1298 connected to patients body, allowing the differential input operations?

Regards,

Ilia V. Davidov

Hi Ilia,

I will look into the other document discrepancies you mentioned. 

The ADS1298 has true differential inputs, so with the configuration described above, you should see +1.5V if the (-) terminal of the battery is placed on IN1N and the (+) terminal of the battery is on IN1P.  Flip the battery terminals around, and you will see -1.5V.  If you do not tie the battery to AGND of the ADS1298, it will be measured as a differential voltage between the INP and INN terminals of the ADS1298.

Assuming your reference is set for 4V, and you replace that battery with a bench power supply, you will be able to apply 4V before you see the display start to saturate.  If you take the AINN termainal of the ADS1298 to AGND, leaving the 4V input on AINP, the display will saturate around 2V.  By grounding the AINN, you will effectively half the input range of the ADS1298.  If your intention is to measure only positive voltages, you should consider using 5V and GND as the AVDD and AVSS rails, level shifting the inputs to VREF/2 to maintain full dynamic range of the ADC.

Hi Tom,

Thanks again :)

Everything is clear for me about the differential input of ADS1298, only one question: "How does connecting of AINN to AGND help to reduce 50Hz noise while measuring the AA battery?" [UPDATED: Let me try to answer to myself. I was wrong. It seems that connecting of AINN to AGND doesn't significally reduce the noise - I've carefully tested this again. When I measured it before, I didn't take in mind that the the software implements autoscale. So you need to look at the left scale (or use Scope analysis tool) to make the decision if the noise level high or low.]

But the problem appears: something strange with PGA&measured results. I have AA rechrgable battery (1.3V) connected to CH2. When I set PGA to 1, I succesfuly measure around -1.3V (as I've connected (+) pole to CH2N). When I set PGA to 2, I see the signal around -0.99 (why not -2.6V=PGA*VIN=2*(-1.3) ?) When PGA is set to 3, the measured signal is around -0.75 (when I was waiting for a semi-full scale (wile VREFP=4.0V)) and so on... The question is traditional :) WHY?

In brief, the results for different PGA's and the same battery on CH2 & VREFP=4V. (I've reconnected (+) to CH2P):

PGA=1, MeanV=1.37, Vrms=25,82e-6

PGA=2, MeanV=1.05, Vrms=63,37e-3 (<-RMS rises UP)

PGA=3, MeanV=0.789, Vrms=47.63e-3 (??)

PGA=4, MeanV=0.631, Vrms=38.17e-3

Hi Ilia,

Will look at this in the lab tomorrow.  Something sounds wrong here so I'll charge up my battery tonight and give it a look over in the morning...

Hi Tom,

Have you charged up your battery already? ;)

Regards,

Ilia

Hi Ilia,

Sorry for the delay in getting back to you.  Please do me a favor and check the jumper positions on JP2 and JP24.  The jumper on JP2 should be on pins 1-2 and the one on JP24 should be on pins 2-3.  Also measure the voltage difference between test points 6 and 13 - it should be 5V (ref TP6, measure TP13).  Also check the voltage difference from TP6 to TP3 - this should be your 4V reference.

The numbers you are getting sound like you have the ADS1298 configured for for 3V operation - you can still set the register for 4V, but you can't get a 4V reference input with a 3V supply.  This will distort your readings.

Hi Tom,

Please take a look at these photos. As you see, everything is OK with VREFP - it is +4.0V relative to AVSS. Even more - I've connected Lion battery (+3.9V) and it successfuly measures it with PGA=1. If I set PGA to 2 it saturates and shows 2V, RMS=0

So any other ideas, please? :) (Why does PGA work abnormally while measuring 1.5V and set PGA=2 ?)  May be the problem still exists :)

[It seems I have an answer to this question! Please check it. Frontend software just shows the voltage applied to the input terminals, not the voltage that comes to ADC's input after the amplifiers. When ADC gets saturated (beacuse I've applied +3.8V to CH2) and PGA was 2, the software shows the saturation at 2V level (as it gets "all ones" frome ADC and also knows that the full scale is 4V, and if PGA=2 then saturation comes while +2V or more applied to channel). So everything seems fine :) ]

BUT WHY WHEN VIN=1.4, PGA=2, it shows 1.05, not 0.7?

Regards,

Ilia

1.Jumpers: JP24[2-3] & JP2[1-2]

2.AVDD to AVSS = +5V

3. VREFP=+4V rel. to AVSS

4.The battery is attached to CH2P,CH2N:

PGA=2, MeanV=1.05, Vrms=63,37e-3

Thanks for the pictures Ilia,

You are correct, the software just shows the voltage applied to the input terminals, not the voltage that comes to ADC's input after the amplifiers.  The display in the scope or histogram is input referred - we are considering add the option to show the voltage based on ADC output code.  Maybe a button that lets you show the voltage based on the ADC output code versus the applied input. 

The floating battery test I think is giving you problems due to perhaps the common mode input range of the device.  With the PGA=1, you are looking at 1.55V>CM>-1.55.  At PGA=2, that drops to ~+/-0.8.  Offset can change a bit with gain as well which will impact this reading.  Try using a couple high value resistors tied in series with the +/-terminals of the battery.  Take the center point to GND and re-run your tests.

With G = 1, 2 or 3 the Mean should be 1.30V, ~47uVrms and ~290uVpp.

Hi Tom,

Thanks a lot - I'll try to check your method of measuring and will report the result. Please explain, how is "CM voltage problem" solved in case of real ECG and patient as the source of input voltage? Where are these "high value resistors" to AGND in real life in 10 wires of standard 12-lead ECG?

Regards,

Ilia

Hi Tom,

I've tried your way - it works! :)

Please check if I right:

• In case of real ECG the common mode voltage is an average voltage of human body relative to AGND of ECG device. (?)
• It may be represented as voltage of WCT (for example) relative to AGND of ADS1298.(?)
• RLD is used to drive the patient's voltage (rel. to AGND) to make this voltage (averaged common voltage) suitable with ADS1298 specifications. So "high value resistors" are represented as RLD electrode.(?)
• One of the possible ways of getting CM to permitted range is to simply connect the patient's body (e.g. via his right leg, or maybe using large metal plate under the patient's back) to AGND of ADS1298 (?)

Waiting for your comments.

Regards,

Ilia

Hi Ilia :-)

I'm a beginner ecg processing (particularly hardware part) and a student.

I read posts of you and Tom.  (but i did not fully understand ;; )

But, your little comments is a great help to me. <- i'm using google's translation :)

I'm using ADS1298ECGFE_PDK and I want to get the ECG signal from my body.

And I want to use just three electrodes for LEAD I ( LA, RA) or LEAD II (LL, RA).

So, I connect pin 9, 10, 11 ( there is J1, ADS1298ECGFE_PDKit) to my body.   ( is it right? )

And I set the channel control registers ( CH2, CH3 -> normal Operation, PGA Gain 1, Channel Input is Normal Electorde, the rest CHn is set power-down)

And last, i'm not use WCT, RLD, and battery.

 Ilia, Can i get the correct ecg signal using only just three electrodes, if your answer is "OK", give me a some comment  ^^;

My question post url =  http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/p/73696/268351.aspx#268351 

Waiting for your comments.

Regards,

On the other side of the earth, Jaein Kim :-)

Hi, Jaein Kim :)

Jaein Kim said:

And I want to use just three electrodes for LEAD I ( LA, RA) or LEAD II (LL, RA).

So, I connect pin 9, 10, 11 ( there is J1, ADS1298ECGFE_PDKit) to my body.   ( is it right? )

And I set the channel control registers ( CH2, CH3 -> normal Operation, PGA Gain 1, Channel Input is Normal Electorde, the rest CHn is set power-down)

And last, i'm not use WCT, RLD, and battery.

 Ilia, Can i get the correct ecg signal using only just three electrodes, if your answer is "OK", give me a some comment  ^^;

In order to get the ECG in one of non-augmented lead (i.e. Lead I, II or III)  you need only 2 electrodes: for lead I  they are LA (pin 10) and RA (pin 9), lead II=LL-RA and lead III is LL-LA. In ideal world :) it's enough to just take pin 10 wire to your left arm and 9 to your right arm. As your _ideal_ ADC has true differential input (in any range, as it's ideal) you'll get (in this case) the value of Lead I ECG.

Unfortunately, in real world your ADC works like differential only when the common-mode voltage (INxP-INxN)/2 is in range, described in document SBAS459E, page 23. In general case this rule is violated due to great noise level and different values of absolute potentials of our body and the AGND of ADS1298. To solve this problem the RL electrode is used. The minimal way, you should do to get something :) that will sound like ECG in Lead I, is to connect the AGND of your board to your right leg. In this case you'll tie the CM voltage to AGND.

But the best approach is to use RLD circuit of ADS1298. Doing so, you'll allow ADS1298 to drive the potential of the body and correct the CM dynamically.

To analyze the source of the noise, please take a look at your signal's spectrum. I'm sure you'll see peaks at frequencies (50Hz x N) |or 60Hz, depends on your outlet's freq. on "the other side of the earth";) You may fight against this noise using digital processing (filters) like in ADS1298ECG GUI is done or make some filter circuits on inputs.

In this case try to power your board from battery - but frankly speaking this doesn't help much.

In nearest future (after weekend) I'll try to give you my ECG in Lead I :)

Please remember that all your movements during the measuring of ECG impacts on result - so it's a good idea to ask your best friend "to play a clinical hospital" :) for some time - when you'll adjust the board and measure the ECG, your friend should lay as quite as possible.

If you'll have any questions, please feel free to ask me.

Regards,

Ilia V. Davidov

p.s. Please note: you SHOULD provide very good contact between your (or your friend's) skin and electrodes. Wet them with salt water etc. than firmly fix them on the skin. [Or even (not recommended :) but I've tried this) you may take the RL electrode to your mouth :) ]

Jaein,

you may want to read page 8, 1.1 here. As far as I know this design is not isolated. What you are trying to do is extremely dangerous and can easily kill you.

Thanks, JustGreg - you're quite right! The design is not isolated - so in worst case outlet voltage can be present on it's parts. When you touch it when it's connected to PC (or even just to outlet using it's AC/DC converter) - you're doing it at your own risk! But I'm lucky - and still alive :) You may also safely work with battery-powered kit connected to battery-powered notebook - in this case module is isolated from dangerous high voltage.

Hi Ilia~

Thank you very much :) Ilia

Sorry for my late comments.

I done my work, I Just followed your comment. And I got the signal.  : )

I connected RA and LA to Pin 9, and 10. And LL(or RL) is connected to AGND of ADS1298 (please, see the picture)

 it is my ecg signal :)

I want to say much to you about WCT and noise problem etc.., but it's very difficult for me using english. T.T

But I'll trying using english and keep contacting with you~ : )

I really thank you about your sincere comments.

And I accept your friendship request, of coures :) Thank you again for your friendship request.

Have a good day~ Ilia :)

Regards, Jaein Kim.

Hi, Jaein,

I'm very happy for you :) My congratulations to you!

If you need some assistance with ADS1298 please feel free to contact me via E2E.TI.COM or directly to idc000(at)gmail.com

As I've already have some experience with this chip (special thanks to Tom Hendrick, Juergen Petruschke, TI, TI Europe & TI Russia) I will be very happy if my knowledge will be usefull for somebody.

Regards,

Ilia

Hi Jaein,

I want do the same like you. My english is very bad too. If you are from germany, you can answer in german.

I want to ask you: Can you send me screenshots from your four ADC Registers (Channel Registers, LOFF and RLD, GPIO and OTHER Registers, Register Map)?

I was very happy when you can do it.

Another problem is: When I press the continous button the GUI do nothing more??? Have you a tip for me?

Best Regards,

Heinrich Reimer

Hi Heinrich :)

Unfortunately, I'm not from germany;;

I'm begginer , and have bad english too ..  :-)

but I hope my comments be a help to you :)

you can see the Registers state in this url. I think it maybe default setting.

http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/p/73696/269746.aspx#269746

In that url, please see the input line, red/white/black line (red line's position is wrong )

If you want to get ECG data from RA LA And LL(or RL),

RA line is connected to Pin9 and LA is connected to Pin10,

And for reference signal, LL(RL) line is connected to TP1(or TP2 or TP11 or  TP12)

And In application program, in Channel Registers, except "input channel 2", all channel power off. (userguide page 45)

then will be work.

When you press the "continous", the GUI (signal display) is refreshed continously.

hmm I'm sorry for my bad english ;)

Regards,

Jaein Kim.

Hi Jaein,

thank you very much for your quick answer.

I do all what you have said and I get very good signals =) thank you.

But I get only a Signal when I connect RA, LA, RL and LL, it is possible to get good signals only from RA and LA???

And what I want to say: Your english is very good i think :-)

Regards,

Heinrich Reimer

Guten morgen~ Heinrich :-)

I'm happy for your work done.

I think that it is impossible. If you do not connect reference signal(RL or LL) to ADS1298, you can't get a right signal.

But if you make artificial reference signal, it may be possible..

See you later Heinrich~

Regards,

Jaein Kim.

Good moring Ilia :)

How are you doing with your work?

I'm working for connecting ADS1298 with CC2540 :)

But it is hard work for me. Originally, my major is DATABASE and DATA Mining

So, hardware is very hard work for me..

Take care, Ilia ~ :)

And when I get a problem, I will tell you first :-}

See you ~ Ilia

Hi folks!

Let me say some words about the "reference electrode": if you're going to use your ECG data for medical diagnostics using standard methodics, then you SHOULD use the RL as a reference ground, otherwise (if you use LL or some other point of your body as reference) your measurements' results will not be applicable (will have different waveforms) for standard methodics.

To Jaein Kim:

Please contact me via e-mail idc000@gmail.com , I have some questions about your project - may be I can participate, if you want. As I've understood you're working on wireless data collecting system - I have some experience in this area (unfortunately, it's not based on TI's & Chipcon solutions - so we can learn it together)

To Reimer Heinrich:

I've answered to your letter, if you need any additional assistance - feel free to contact me.

Regards,

Ilia Davidov

Hi Rita Kasha,

As far as I know,  you can't get continuous data flow (or picture, as it's the same) using standard LabVIEW-based software for MMB0. In order to get what you want you have to implement your own interface between ADS1298 daughterboard and your PC. Also you need to write your own application for PC that will get the dataflow from ADS1298 and analyze or may be draw it as you want.

The hardware part of this custom interface may be based on simple MSP430-based MCU whith USCI in SPI mode connected to ADS1298 and USART connected to PC's COM-port via level-shifters.

Regards,

Ilia

Ilia,

thank you so much for replying back so quick!! I am trying to get( Lead I) reading...so i'm powering down all the other channels except 1,2, and 3 (in the software), but i am getting a lot of noise and also I am getting waves (on the ECG tab display) from the rest of the leads (leads II, III...etc)...I am connecting RA to my right arm LA to my left arm and RL to my right leg....do you know how I can reduce the noise and get a nice signal like the figures shown earlier in this post?

I am turning the notch filer option on but no improvement :(

Thanks again for ur help:)

Please take a look at my post in this thread from 19 Nov 2010 9:24 AM - I've published there full "HOW-TO" of getting simple ECG from body.

Feel difference between ECG lead and ADS1298's channel. In most cases ECG lead is formed from one channel and WCT, which (WCT) is a production of some other channels. Pleas note that if you've switched some channels off, they should give you zeros on "Scope" view but on "ECG Display" you'll see "waves" as Leads are shown there but not channels.

As you can read in mentioned post, the best way to reduce noise is to use RLD circuit (also you should turn on the RLD source in ADS1298). In order to decide what kind of noise do you have, please also take a look on it's spectrum - if it's 50/60Hz outlet frequency? Or something else?

Hope this will help you to see your heartbeat :)

I did look at the post and I followed what u said...however i am still having trouble with noise...and really i'm not even getting the right wave...is there a special option in the software for setting the RLD circuit? (in the "Right leg derivation control registers" under the "ADC Register" then "LOFF and RLD" tab) do I need to change these. because right now what i'm doing is connecting my right leg wire to TP 11 on the board and RA LA are in the appropriate pins!

thanks for ur help:) but this is really frustrating and I would really appreciate ur response!

As I see, TP11 is AGND, while your right leg should be connected to pin 14 of J1 (ELEC_RL) in order to make RLD functionality to work.

Now remove JP30-JP34, JP37 - lets leave only JP35,JP36 - ECG_LL,ECG_RA,ECG_LA are now connected to IN2N, IN2P, IN3N, IN3P.

We need these leads (LL,LA,RA) in order to produce RLD signal.

You may also short removed channels, setting removed jumpers between 2&4 pins.

Now in software:

1.Globally set all channels to powered down state.

2.Enable CH2,CH3 by setting them to Normal Operation state.

3.Set RLD functionality as shown on Fig.52,53 of SBAU171.

4. You may try to start your experiments at lower gain (1).

Power your board from batteries.

After all this is done, securely connect leads to your body, use salt water or special gel with electrodes to make contact better. Don't move while measuring - this will impact the result (it's better to ask your friend to assist you).

Now try to get the result. Keep in mind that ECG stabilizes during at least 15-20 seconds after starting of measurements.Also use FFT filter for outlet frequency.

Hope this will help you. If not - please post your results here, I'll try to comment them.

Hi Ilia, I was working on other projects and now I'm back to working on the ECG project again!! I can't thank you enough for responding and trying to help me :) I actually followed the steps from your last message and now I am getting something but it's still not a clear picture. I have a few questions please. first when I hook up the wires to my arms and press CONTINUOUS on the software...then I go to "ECG DISPLAY" tab...it still shows me multiple plots and they're all mixed together....I only want to see "LEAD I" but it still gives me plots for all the other leads too even though I only turned on channels 2 and 3 so I am only getting data from RA, LA and LL. also it won't let me save data or figure so I am not sure how to post the picture that I am getting so you can see it...... any suggestions please??

Hi Rita Kasha,

On "ECG display" tab you see all leads because this tab is designed this way :) It doesn't allow to turn off some leads. But you may analyze separate lead  in new window - just click on its waveform and this waveform will open in it's individual window.

Please remember that ADS1298 channels ARE NOT THE SAME THINGS as ECG LEADS. Please feel this difference! You may turn off (short input) channels but not leads - but leads will still be calculated and shown on the ECG tab. Take a look at Table 26,p.45 of SBAU171. As you may see, if you enable at least LA,RA electrodes while all others are 0, you'll get: LI=LA-RA - this is what you want to see,but for others: V(1..6)=-(RA+LA)/3, LII=-RA - not zeros, but some waveform produced from LA,RA.

In order to publish screens here you may use PrtSc (Print Screen) key - just press Print Screen on your keyboard, this will place current view of your screen to clipboard, then you may paste (CTRL+V) it to  your favorite graphical editor like Paintbrush ("Start" - "Run" - "pbrush.exe"), then you may save it as a picture and attach to this forum.

Regards,

Ilia