Datasheet

 1996 Microchip Technology Inc. DS30430B-page 33
PIC16F8X
7.0 DATA EEPROM MEMORY
The EEPROM data memory is readable and writable
during normal operation (full V
DD
range). This memory
is not directly mapped in the register file space. Instead
it is indirectly addressed through the Special Function
Registers. There are four SFRs used to read and write
this memory. These registers are:
• EECON1
• EECON2
• EEDATA
• EEADR
EEDATA holds the 8-bit data for read/write, and
EEADR holds the address of the EEPROM location
being accessed. PIC16F8X devices have 64 bytes of
data EEPROM with an address range from 0h to 3Fh.
The EEPROM data memory allows byte read and write.
A byte write automatically erases the location and
writes the new data (erase before write). The EEPROM
data memory is rated for high erase/write cycles. The
write time is controlled by an on-chip timer. The
write-time will vary with voltage and temperature as
well as from chip to chip. Please refer to AC
specifications for exact limits.
When the device is code protected, the CPU may
continue to read and write the data EEPROM memory.
The device programmer can no longer access
this memory.
7.1 EEADR
The EEADR register can address up to a maximum of
256 bytes of data EEPROM. Only the first 64 bytes of
data EEPROM are implemented.
The upper two bits are address decoded. This means
that these two bits must always be '0' to ensure that the
address is in the 64 byte memory space.
FIGURE 7-1: EECON1 REGISTER (ADDRESS 88h)
U U U R/W-0 R/W-x R/W-0 R/S-0 R/S-x
— — — EEIF WRERR WREN WR RD R = Readable bit
W = Writable bit
S = Settable bit
U = Unimplemented bit,
read as ‘0’
- n = Value at POR reset
bit7 bit0
bit 7:5 Unimplemented: Read as '0'
bit 4 EEIF : EEPROM Write Operation Interrupt Flag bit
1 = The write operation completed (must be cleared in software)
0 = The write operation is not complete or has not been started
bit 3 WRERR : EEPROM Error Flag bit
1 = A write operation is prematurely terminated
(any MCLR
reset or any WDT reset during normal operation)
0 = The write operation completed
bit 2 WREN : EEPROM Write Enable bit
1 = Allows write cycles
0 = Inhibits write to the data EEPROM
bit 1 WR : Write Control bit
1 = initiates a write cycle. (The bit is cleared by hardware once write is complete. The WR bit can only be
set (not cleared) in software.
0 = Write cycle to the data EEPROM is complete
bit 0 RD : Read Control bit
1 = Initiates an EEPROM read (read takes one cycle. RD is cleared in hardware. The RD bit can only be
set (not cleared) in software).
0 = Does not initiate an EEPROM read
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