EEPROM Write Cycle- Does it Hog the PIC's time?

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Hi

A newbie question on EEPROMs:

I have the following subroutine:

void pageWrite_ext_eeprom(long int address, byte mask){
int ik;
START:
i2c_start();
if(i2c_write(0xa0 | mask)!=0) //Device must ACKNOWLEDGE
goto START;
i2c_write(address>>8); //High Byte of Address
i2c_write(address&0X00FF); //Low Byte of Address
for(ik=0;ik<PAGE_SIZE;ik++){ //Write Page to EEPROM
i2c_write(dat[ik]);
}
i2c_stop();
}

The datasheet of 24LC256 says that when "stop" is written to the EEPROM, the EEPROM starts writting the data in the page to memory- this it says will take a maximum of 5ms.

My question is: how long (how many Xstal "ticks") will the above routine take?
when the i2c_stop() is executed, will the PIC require a further 5ms before the subroutine returns?

Thank you in advance for your help.
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[valemike]

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Hi Valemike

Thank you for your reply- ok so the i2c_stop() is not hogging the time.
Can you please tell me how long the whole subroutine will take to execute? (I am using a 4MHz Xstal). and PAGE_SIZE=16

Once again thank you
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void pageWrite_ext_eeprom(long int address, byte mask){
int ik;
START:
i2c_start();
if(i2c_write(0xa0 | mask)!=0) //Device must ACKNOWLEDGE
goto START;
i2c_write(address>>8); //High Byte of Address
i2c_write(address&0X00FF); //Low Byte of Address
for(ik=0;ik<PAGE_SIZE;ik++){ //Write Page to EEPROM
i2c_write(dat[ik]);
}
i2c_stop();
}

[Ttelmah]

The easiest way, is to run the routine in a simulator, and use the 'stopwatch' ability. The time will depend mainly on the I2C rate chosen, which you do not state.
Also if the chip at the other end of the I2C bus is 'busy' at the start, the code will wait in the initial loop for the acknowledge. Assuming that this does not occur, there will be 19 I2C transfers, each taking about 95uSec (at 100K I2C, and assuming the MSSP BRG value is correctly set for this, and depending on how long the slave holds the 'ack' line on each transfer). Probably about 2mSec.

Best Wishes

[Guest]

Hi Ttelmah

Thank you for your post.
I am not sure how to set the clock speed on the i2c.

At the top of the file I have:

#use i2c(master,sda=EEPROM_SDA, scl=EEPROM_SCL)

but there is no reference to clock speed on the i2c.
I have 2 2.2k pull up resistors on the EEPROM.

I would be really thankful if you can tell me how to set the clock speed.
(The faster the better).
I am using the LF pic's and running off a 3.3V power supply.

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[Ttelmah]

#use i2c(master,sda=EEPROM_SDA, scl=EEPROM_SCL,FAST)

The default I2C specification, is 100KHz clock. There is a fast defintion at 400Khz clock, and adding the 'FAST' keyword will tell the compiler to try to program closer to this faster rate. Going beyond this, will depend on the version of your compiler. The 'general purpose' way, is to define the address of the I2C BRG as a BYTE variable, and set it yourself. The other method only applies to the latest compilers, which allow you to use:

#use i2c(master,sda=EEPROM_SDA, scl=EEPROM_SCL,FAST=800000)

and the compiler will try to program the rate you have specified.
In each case, the 'actual' rate will be limited by the hardware. For a 4Mhz master clock, the fastest rate possible is 1Mhz, and for the 400K specification, the fastest rate possible 'below' this, is 333KHz.

Best Wishes

[jds-pic]

[Guest]

Hi

I am a newbie and dont really know what is a simulator. I would really appreciate it if you give me a step by step example?

Also, Can someone please tell me how long the following code snippet will take in ms?

Thank you in advance
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ChXL = get_timer1();
set_timer1(0);
interL = inter;
inter = 0;
DutyCycle = (float)(ChXH)/(float)(ChXH+ChXL);
DutyCycle = DutyCycle*255;
accel = (int)(DutyCycle);
dat[icnt] = accel;
icnt++;
if(icnt==PAGE_SIZE){
if(iPage==100){
break;
}
dat[0] = prev;
prev = dat[PAGE_SIZE-1];

pageWrite_ext_eeprom(iPage*PAGE_SIZE, mask);
iPage++;
icnt=0;
}
printf("+%x ",accel);

and the pageWrite_ext_eeprom subroutine is:

void pageWrite_ext_eeprom(long int address, byte mask){
int ik;
START:
i2c_start();
if(i2c_write(0xa0 | mask)!=0) //Device must ACKNOWLEDGE
goto START;
i2c_write(address>>8); //High Byte of Address
i2c_write(address&0X00FF); //Low Byte of Address
for(ik=0;ik<PAGE_SIZE;ik++){ //Write Page to EEPROM
i2c_write(dat[ik]);
}
i2c_stop();
}

PS
I have the accelerometer going at about 136Hz.
That means that the T = 7.35ms
Say the high time = the low time (approximately true), then I will have 7.35/2 = 3.68ms to perform the above tasks (Xstal = 4MHz, i2c running on the slow speed, using software, RS232 baud=19200).

[Ttelmah]

[Guest]

Hi Ttelmah

I understand what you write- that the EEPROM can be writting and the PIC can be doing something else in parallel.

However, it seems that the code I have posted above is taking longer than approximately 4ms. Can you please tell me if you think that the above code should be taking 4ms?
Is there a problem with the dat[] array?

All the best
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