PIC18F2420/2520/4420/4520
FIGURE 6-2:
TABLE WRITE OPERATION
Instruction: TBLWT*
Program Memory
Holding Registers
(1)
Table Pointer
Table Latch (8-bit)
TABLAT
TBLPTRU TBLPTRH TBLPTRL
Program Memory
(TBLPTR)
Note1: The Table Pointer actually points to one of 32 holding registers, the address of which is determined by
TBLPTRL<4:0>. The process for physically writing data to the program memory array is discussed in
Section 6.5 “Writing to Flash Program Memory”.
The FREE bit, when set, will allow a program memory
erase operation. When FREE is set, the erase
operation is initiated on the next WR command. When
FREE is clear, only writes are enabled.
6.2
Control Registers
Several control registers are used in conjunction with
the TBLRDand TBLWTinstructions. These include the:
• EECON1 register
• EECON2 register
• TABLAT register
• TBLPTR registers
The WREN bit, when set, will allow a write operation.
On power-up, the WREN bit is clear. The WRERR bit is
set in hardware when the WR bit is set and cleared
when the internal programming timer expires and the
write operation is complete.
6.2.1
EECON1 AND EECON2 REGISTERS
Note:
During normal operation, the WRERR is
read as ‘1’. This can indicate that a write
operation was prematurely terminated by
The EECON1 register (Register 6-1) is the control
register for memory accesses. The EECON2 register is
not a physical register; it is used exclusively in the
memory write and erase sequences. Reading
EECON2 will read all ‘0’s.
a
Reset, or
a write operation was
attempted improperly.
The WR control bit initiates write operations. The bit
cannot be cleared, only set, in software; it is cleared in
hardware at the completion of the write operation.
The EEPGD control bit 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.
Note:
The EEIF interrupt flag bit (PIR2<4>) is set
when the write is complete. It must be
cleared in software.
The CFGS control bit determines if the access will be
to the Configuration/Calibration registers or to program
memory/data EEPROM memory. When set,
subsequent operations will operate on Configuration
registers regardless of EEPGD (see Section 23.0
“Special Features of the CPU”). When clear, memory
selection access is determined by EEPGD.
DS39631E-page 74
© 2008 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
