>On Mon, Apr 3, 2023 at 10:53?AM Bo Berglund via fpc-pascal < >fpc-pascal@lists.freepascal.org> wrote: > >> On Mon, 3 Apr 2023 08:42:12 -0400, "Jeffrey A. Wormsley via fpc-pascal" >> <fpc-pascal@lists.freepascal.org> wrote: >> >> >> >> >> i2c_read_reg works too inasmuch as it does not error out, but it >> returns FF >> >> whatever addres I read like the i2c-tools command does. >> >> I am not sure that it is correct though... >> >> >> > >> >Yes this is expected, as eeproms erase to $FF. You can write to the same >> >byte as many times as you want, as long as you only change 1 bits to 0 >> >bits. If you must change a 0 bit to a 1 bit, you have to erase back to >> $FF >> >first. Be aware that erase means erasing the entire page, and not just a >> >single byte. This is where things like "wear leveling" come into play, >> >because a page can only be erased a limited number of times (it used to be >> >around 10,000, but maybe newer devices have extended this). How you >> manage >> >writes to eeprom can be tricky, best to use them for things that don't >> >change very often, such as configuration data. >> > >> >Jeff >> > >> >> This is incorrect! >> The EEPROM I am talking about is a small 8-pin chip specifically used in >> IoT >> devices to save non-volatile data and these devices are r/w on single >> bytes. >> >> I have just tested it by executing command line commands to write a set of >> data >> to a specific address and then read it back and verified that it was there. >> Then I repeated the process for the same addresses but different data. >> Readback again showed only the new data correctly. >> >> What you are talking about might be certain microcontrollers which >> simulate an >> EEPROM memory in their flash program memory data. That flash is commonly >> erasable only for full pages. Not the case here... >> >> I am working on using the FreePascal GitHub code and expanding it into a >> class I >> can use in my RPi4 project. Since I want to generalize it as much as >> possible it >> takes a few more hours than I thought... >> On Mon, 3 Apr 2023 14:26:17 -0400, "Jeffrey A. Wormsley via fpc-pascal" <fpc-pascal@lists.freepascal.org> wrote:
>I've been using i2c and SPI eeproms for almost two decades. All of them >can read/write a single byte if that's what you want to do, but the >write/erase restrictions I noted are there for any parts I've ever used. >If you write a byte to $00, you cannot write it to $01 without first >erasing the entire block that it is located in (usually 128 to 256 bytes). >You can write $FF to $F0, then $F0 to $80, then $80 to $00, as these all >only involve turning 1 bits into 0 bits, but if you try to write from a $00 >to a $01, then it will not work, at least not on any part I've ever used, >as that involves turning a 0 bit into a 1 bit. All of the parts I've >seen, if you want to modify a single memory location (if the write involves >turning a 0 bit into a 1 bit), they require you to read the block of data >into your CPU, modify it there, erase the block, then write the entire >block data back into the chip. I've seen some parts that have an on-chip >RAM buffer that would let you read the block into this RAM buffer with one >command, modify the RAM buffer with a single byte write, erase the block, >then write the RAM buffer back to the chip, which is a lot faster than >having to do this yourself with your CPU memory, but it still required the >block erase and that block erase still counted towards your maximum number >of erase cycles. I have not seen a chip that allowed completely random >writes at the byte level before short of a static ram with battery backup. > >If you have an i2c part that doesn't work like this, then I would be very >interested in knowing the part number and seeing a link to the data sheet. >Such a part would make using these sorts of devices much easier, but to >date I have never seen one. > >Jeff > I just tested by writing four 0x00 bytes in a row, then verifying that the memory read shows these, then writing other data and again verifying that the data is there. All using the i2c-tools commands: $ i2ctransfer -y 1 w6@0x50 0x00 0x00 0x00 0x00 0x00 0x00 $ i2ctransfer -y 1 w2@0x50 0x00 0x00 r8@0x50 0x00 0x00 0x00 0x00 0xff 0xff 0xff 0xff $ i2ctransfer -y 1 w6@0x50 0x00 0x00 0x70 0x30 0x55 0x40 $ i2ctransfer -y 1 w2@0x50 0x00 0x00 r8@0x50 0x70 0x30 0x55 0x40 0xff 0xff 0xff 0xff The part number is: CAT24C32 by ON Semiconductor (www.onsemi.com) It is a 128 kbit (16 kbyte) part organized as 64 pages of 256 bytes. -- Bo Berglund Developer in Sweden _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
