PIC16F7X7
3.3
Reading the Flash Program
Memory
3.4
Operation During Code-Protect
Flash program memory has its own code-protect
mechanism. External read and write operations by
programmers are disabled if this mechanism is
enabled.
A program memory location may be read by writing two
bytes of the address to the PMADR and PMADRH reg-
isters and then setting control bit, RD (PMCON1<0>).
Once the read control bit is set, the microcontroller will
use the next two instruction cycles to read the data. The
data is available in the PMDATA and PMDATH
registers after the second NOPinstruction; therefore, it
can be read as two bytes in the following instructions.
The PMDATA and PMDATH registers will hold this
value until the next read operation.
The microcontroller can read and execute instructions
out of the internal Flash program memory, regardless
of the state of the code-protect configuration bits.
EXAMPLE 3-1:
FLASH PROGRAM READ
BSF
BCF
STATUS, RP1
STATUS, RP0
ADDRH, W
PMADRH
ADDRL, W
PMADR
;
; Bank 2
;
MOVF
MOVWF
MOVF
MOVWF
BSF
; MSByte of Program Address to read
;
; LSByte of Program Address to read
; Bank 3 Required
STATUS, RP0
Required
Sequence
BSF
NOP
NOP
PMCON1, RD
; EEPROM Read Sequence
; memory is read in the next two cycles after BSF PMCON1,RD
;
BCF
MOVF
MOVF
STATUS, RP0
PMDATA, W
PMDATH, W
; Bank 2
; W = LSByte of Program PMDATA
; W = MSByte of Program PMDATH
TABLE 3-1:
REGISTERS ASSOCIATED WITH PROGRAM FLASH
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
Value on
all other
Resets
Value on:
POR, BOR
Address Name
Bit 0
10Dh
10Fh
10Ch
10Eh
18Ch
PMADR EEPROM Address Register Low Byte
PMADRH
PMDATA EEPROM Data Register Low Byte
xxxx xxxx uuuu uuuu
—
—
—
—
EEPROM Address Register High Byte ---- xxxx ---u uuuu
xxxx xxxx uuuu uuuu
PMDATH
—
—
—
EEPROM Data Register High Byte
--xx xxxx --uu uuuu
PMCON1 reserved(1)
—
—
—
—
—
RD 1--- ---0 1--- ---0
Legend: x= unknown, u= unchanged, — = unimplemented, read as ‘0’. Shaded cells are not used during Flash access.
Note 1: This bit always reads as a ‘1’.
DS30498C-page 32
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
