PIC18F242 MICROCHIP [Microchip Technology], PIC18F242 Datasheet - Page 58

• Manufacturer Part Number: PIC18F242
• Description: 28/40-pin High Performance, Enhanced FLASH Microcontrollers with 10-Bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18FXX2
FIGURE 5-2:
5.2
Several control registers are used in conjunction with
the TBLRD and TBLWT instructions. These include the:
• EECON1 register
• EECON2 register
• TABLAT register
• TBLPTR registers
5.2.1
EECON1 is the control register for memory accesses.
EECON2 is not a physical register. Reading EECON2
will read all '0's. The EECON2 register is used
exclusively in the memory write and erase sequences.
Control bit EEPGD determines if the access will be a
program or data EEPROM memory access. When
clear, any subsequent operations will operate on the
data EEPROM memory. When set, any subsequent
operations will operate on the program memory.
Control bit CFGS determines if the access will be to the
configuration registers or to program memory/data
EEPROM memory. When set, subsequent operations
will operate on configuration registers, regardless of
EEPGD (see “Special Features of the CPU”,
Section 19.0). When clear, memory selection access is
determined by EEPGD.
DS39564C-page 56
Note 1: Table Pointer actually points to one of eight holding registers, the address of which is determined by
Control Registers
TBLPTRU
EECON1 AND EECON2 REGISTERS
TBLPTRL<2:0>. The process for physically writing data to the Program Memory Array is discussed in
Section 5.5.
Table Pointer
TBLPTRH
TABLE WRITE OPERATION
(1)
TBLPTRL
Program Memory
(TBLPTR)
Instruction: TBLWT*
Holding Registers
Program Memory
The FREE bit, when set, will allow a program memory
erase operation. When the FREE bit is set, the erase
operation is initiated on the next WR command. When
FREE is clear, only writes are enabled.
The WREN bit, when set, will allow a write operation.
On power-up, the WREN bit is clear. The WRERR bit is
set when a write operation is interrupted by a MCLR
Reset or a WDT Time-out Reset during normal opera-
tion. In these situations, the user can check the
WRERR bit and rewrite the location. It is necessary to
reload the data and address registers (EEDATA and
EEADR), due to RESET values of zero.
Control bit WR initiates write operations. This bit cannot
be cleared, only set, in software. It is cleared in hard-
ware at the completion of the write operation. The
inability to clear the WR bit in software prevents the
accidental or premature termination of a write
operation.
Note:
Interrupt flag bit EEIF, in the PIR2 register,
is set when the write is complete. It must
be cleared in software.
© 2006 Microchip Technology Inc.
Table Latch (8-bit)
TABLAT