how much time takes to read a character from eeprom

binu kr · Guest

please help me to know

k=read_eeprom(0);
how much time takes the function to read a character from eeprom of pic micro controller..pic16f877a

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

Well, as far as time wise goes, it depends on your crystal speed. Here's the code that was generated in an 18F2525:

Ttelmah · Guest

Key is though, that reading is almost instantaneous. You just have to load the address required, trigger the read access bit, and read the data. It is _writing_, that is slow on EEPROM type memory. The code shown, just does the work to load the address, trigger the read, and retrieve the data.
This is basically the same as for the 'flash' memory in the chip, which also takes similar time to write (between 1 and 8mSec, depending on the chip - 4 to 8, on the 877), but reading is done for every instruction, without needing delays, even at 48MHz clock rates. This is why there is not a figure specified in the data sheet for the read.
So, if you need to know the exact time, for something very timing critical, count the instructions, as rnielsen says. However for normal use the time is short enough to not matter.

Best Wishes