Peace to all,

How do we implement it in assembly?

Say I want to jump if Accumulator is greater than 27D?
Is there a fool-proof way of doing it?

At the moment I am checking the Accumalator say for 28D, and when it reaches it I jump, this is using CJNE.

But its not giving me a reliable result as it may not be passing 28D due to other cycles being spent before the accululator being checked using CJNE so the 28D value may not be there when the CJNE instruction is being executed (though I have tried to implement ways to ensure 28D is reached on the CJNE instruction).

So is there a proper way to do it? ie. where whatever the value of Accumulator is, as long as it is greater than 28D, it will jump. Suppose it is 35D, it will jump...

Many thanks for your help.

This message board has been a great help!

 

Perhaps you might try mentioning the processor you're using? - if it was a PIC (which it isn't) the PICList has plenty of details.

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Appologies, it is an 8051.

Many thanks.

 

Are you using this method of comparison?

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"There is no way to peace, peace is the way!"

 

You dont have to use the CJNE instruction at all. You can do a subtraction and check the carry flag, which for subtraction is actually a borrow. the following instruction set reference from Atmel has examples in it for this kind of stuff.
http://www.atmel.com/dyn/resources/p...ts/doc0509.pdf

Good Hunting

PS I knew which processor you were talking about. CJNE is kinda unique, and some of us are fortunate to know more than one processor family.

 

kinjalgp, I was not monitoring the carry flag at all.

papabravo, thanks for this method.

This sounds like it will work!

Many thanks.

 

Small detail, don't forget to clear the carry flag before your subb instruction otherwise you will end up with a bug.

Sometimes it work because the carry was cleared by previous instructions
Sometimes it won't work because the carry was set by previous instructions

 

Many thanks.

I am actually programming an 8051 for an ultrasonic rangefinder (SRF05) and trying to use this method to ascertain if the signal from the device has been on for a certain period of time (the length of this signal tells us the range).

Basically above a certain time period, object is out of range. And when within this time period, it is within range.

So far, I have not got it to work as I want!

 

How are you measuring pulse duration? Show your complete code because without that it is difficult to pin-point whats going wrong in it.

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"There is no way to peace, peace is the way!"

 

Did you read this one: http://www.interq.or.jp/japan/se-inoue/e_pic6_6.htm
or this one: http://instruct1.cit.cornell.edu/cou...7/jjl49_mar97/

Should be the starting point of every US porject

How do you generate the US burst?

 

mcs51mc,

SRF05 sends out 8 cycles of U.S. bursts upon a trigger. So all I do is triffer the relevant pin SRF05.

kinjalgp,

I dont have an oscilloscope so I cant test whats going on at the hardware level. At the moment, when I download the program and connect it up on the breadboard, The object detected and object not detected LEDs come on and off randomly regardless of distance of an object in fron of the sensor. Sometimes I notice some consistancy, but it is pretty random most of the time. If I keep an object at close range without moving it, the LEDs keep switching.


Here is the code:

 

Is this correct?
I think your idea is to stay here as long P0.0 is high so you should jump to "REMAIN1" not "REMAIN".
In the mean time T0 is counting 1ms intervals (if you have a 12MHz xtal).

What happens after that line is complete unclear to me.
According to what I read in the SRF05 spec, you should divide the measured time by 58 to get distance in cm. Where is your division?

Unless you just want to know if the US see something and check for 30ms time-out of the SRF05 But even then the sequence is wrong.

Explain your DELAY_FIFTY: routine

 

Firstly sorry for the late reply.

I am not looking to measure any distance numerically to any precision. All I want to do is detect if something is there at close range (at roughly any distance at first) and turn on P1.0 and P1.1 pff if anything is detected, and vice versa if nothing is detected.

If I may run through the MONITOR bit with you... basically, P0.0 is measuring the echo pulse. At REMAIN1 it is checking to see if it still at logic 1, if it is, it jumps to REMAIN. Bear in mind Timer 0 is rolling all this time. At REMAIN, we transfer TL0 into R5.

BTW, the CJNE instruction there is commented out and it not part of the code. We then subtract R5 (which has the the Timer value) from the accumulator which has the decimal 100 in it. At the beginning , 100 minus R5 will give ninety-something as the timer had just started. Carry flag will not be sat. We check to see if carry is not set, if it is not set, we jump back to REMAIN1 to check if P0.0 is still at logic 1. if it is, we again jump to REMAIN and minus the timer value from the accumulator. This time, the timer will have an even larger value, hence the accumulator will decrease by more in this go...if after several cycles of P0.0 being at logic 1 and performing this routine, the accumulator reaches below zero, carry flag is set and detected. It means P0.0 has stayed on for too long and so no object has been detected. P1.1 will be set and P1.0 is cleared.

If P0.0 is detected as low before the the carry flag is detected, it means there is an object there and P1.0 is set and P1.1 is cleared.

I expect the lights to remain constant when a object is fixed in front of the sensors, but they keep alternating; as if the objects kep moving randomly - in and out of range.

About the DELAY_FIFTY, it is not actually delaying for 50 milliseconds, but much longer. This is so that I could see the SFR06 LED flash...I dont have an osciloscope; I wanted to make sure everything happened before I trigger the next one, just until I get it working.

Thanks.

 

Basicly you just want to know if there's something in front of the SRF05. You must drop the "close range" in you first sentence because the SRF05 detects over the complete range (not found in datasheet(?) of SRF05 )

Now I understood your algorithm. But it's too complicated to only detect presence/absence of object

Some problems in you code:
1) 100-TL0 is done only once, next time you pass the SUBB the acc still holds 100-TL0 from previous pass.

2) You have to clear the carry flag before the SUBB instruction

What I would do:
Problem is the accuracy of T0 and the time out value (30ms) of the SRF05. I used 29 but maby you have to adapt this according to the hardware.
To evaluate it you can use the CJNE instruction in combination with the carry flag. That you will have greather, equal and less situations. Put each one on a different output led and see what happen...

This code can easily be modified to calculate the distance to the object.

Please notice that I didn't check that code with the assembler, just typed it while I was thinking, so a typo is always possible

 

Hi there,

thanks for the code...I really appreciate it.

I am going to look at it further to see how I can adapt it to what I need.

But very quickly, the problem I see is that as I am using a crystal of 11.0592MHZ, each cycle is 1.085uS, so for 30ms, I will need 30ms/1.085uS = 27650 cycles which LB of T0 will not represent 2^8=256.

I think I can use HB of T0...(2^16) - (2^8) = 65280 max.; lowest value on HB would be 256, next highest 512 etc.

Thanks again.