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Mic
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| EEPROM or Flash memory ??? |
 Posted: Fri Feb 13, 2004 2:04 am |
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Hello all !
I'm working with a PIC16F877 and I would like to store 100 bytes in memory. Is it better to strore that bytes in EEPROM memory or in FLASH memory ??
I saw in this forum a topic who talk about the #ROM instruction.
Does this instruction store the data in EEPROM or in FLASH memory ?
I use this code (I found it in a topic of this forum). It works but I don't understand why must I start at the address 0x2100 and why must I use the instruction read_eeprom(0) to read the first byte stored ????
| Code: | #ROM 0x2100 = {0x0E,0xB2,0x0F,0x22,0x0C,0xF2,0x0D,0x62,0x0E,0x42,0x10,0x02,
0x0D,0xD2,0x10,0x72,0x11,0x52,0x11,0xC2,0x0F,0x92,0x05,0x72,
0x0B,0x32,0x0A,0xC2,0x06,0x52,0x0B,0xA2,0x0C,0x82,0x14,0x62,
0x15,0x62,0x10,0xE2,0x15,0xE2,0x13,0xF2,0x13,0x12,0x16,0x62,
0x14,0xD2,0x13,0x82,0x12,0x32,0x12,0xA2,0x0C,0x12,0x05,0xE2}
...
...
...
...
...
...
Nh=read_EEPROM(0);
Nl=read_EEPROM(1);
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Can you help me please ????
Sorry for my english ! |
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Ttelmah
Guest
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| Re: EEPROM or Flash memory ??? |
| Posted: Fri Feb 13, 2004 3:22 am |
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| Mic wrote: | Hello all !
I'm working with a PIC16F877 and I would like to store 100 bytes in memory. Is it better to strore that bytes in EEPROM memory or in FLASH memory ??
I saw in this forum a topic who talk about the #ROM instruction.
Does this instruction store the data in EEPROM or in FLASH memory ?
I use this code (I found it in a topic of this forum). It works but I don't understand why must I start at the address 0x2100 and why must I use the instruction read_eeprom(0) to read the first byte stored ????
| Code: | #ROM 0x2100 = {0x0E,0xB2,0x0F,0x22,0x0C,0xF2,0x0D,0x62,0x0E,0x42,0x10,0x02,
0x0D,0xD2,0x10,0x72,0x11,0x52,0x11,0xC2,0x0F,0x92,0x05,0x72,
0x0B,0x32,0x0A,0xC2,0x06,0x52,0x0B,0xA2,0x0C,0x82,0x14,0x62,
0x15,0x62,0x10,0xE2,0x15,0xE2,0x13,0xF2,0x13,0x12,0x16,0x62,
0x14,0xD2,0x13,0x82,0x12,0x32,0x12,0xA2,0x0C,0x12,0x05,0xE2}
...
...
...
...
...
...
Nh=read_EEPROM(0);
Nl=read_EEPROM(1);
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Can you help me please ????
Sorry for my english ! |
Which is 'best', depends on the applicatiion needs. The EEPROM, only offers 256 bytes of storage, so for large tables, the main memory may have to be used. The main emory, has a much more limited number of read/write cycles supported, so if the data needs to be changed at all often, the EEPROM should be used. Using main memory, reduces the code size that you can have.
The instruction to read the EEPROM storage, is 'read_eeprom'. The EEPROM is typically 256 bytes in size, and the instruction simply accepts a number from 0 to 255, as an 'address', and returns the byte at that address in the EEPROM. So 'read_eeprom(0)', returns the first byte from the EEPROM.
The '0x2100', will vary with different types of chip. This is part of the 'programming specification' from MicroChip. To allow the EEPROM to be written by device programmers, it is 'mapped' into the main memory area at an address, during the programming operation. For the 16 family devices, this address is '0x2100', which is above the top of the normal flash memory. For 18 series chips it is 0xF00000.
The ROM statement, puts data at a specific address. So if you used #ROM 0x100=
the following data would appear at address 100 in the main memory. At this address (on chips that support it), the data could be read using the 'read_program_eeprom' instruction. The same instruction, when used to write to 0x2100 (on the chips where the data EEPROM is mapped at this point during programming), puts the data into the data EEPROM instead, and it can then be read with the 'read_eeprom' instruction.
Best Wishes |
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Mic
Guest
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| tell me if i'm right |
| Posted: Fri Feb 13, 2004 4:09 am |
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Thank you very much for your help Ttelmah !
Tell me if I'm right:
if I use #ROM 0x2100 {data....}, I'll store data in the PIC's EEPROM so I'll can store 'only' 256 bytes. The address 0x2100 is the mapped address of the PIC16F877's EEPROM in the main memory area and that's why I can use the read_eeprom() instruction to read the data. |
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Pete Smith
Joined: 17 Sep 2003
Posts: 55
Location: Chester, UK
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| Re: tell me if i'm right |
| Posted: Fri Feb 13, 2004 4:33 am |
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| Mic wrote: | Thank you very much for your help Ttelmah !
Tell me if I'm right:
if I use #ROM 0x2100 {data....}, I'll store data in the PIC's EEPROM so I'll can store 'only' 256 bytes. The address 0x2100 is the mapped address of the PIC16F877's EEPROM in the main memory area and that's why I can use the read_eeprom() instruction to read the data. |
Spot on 
Bear in mind that #rom is a compile time option, which will pre-load the EEPROM data when you program the PIC. It can't be used at a couple of places in your code to load values at different times.
Pete. |
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Mic
Guest
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| ok I'll keep this in my mind ! |
| Posted: Fri Feb 13, 2004 4:41 am |
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Thank you for this precision Pete !
I'll try to keep this in my mind !
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