PIC16CR74ESLASHSP datasheet(32/172 Pages) MICROCHIP

32 / 172 page

PIC16CR7X

DS21993C-page 30

3.3

Reading the ROM Program

Memory

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 regis-

ters after the second NOP instruction. 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.

3.4

Operation During Code-Protect

ROM program memory has its own code-protect mech-

anism. External Read operations by programmers are

disabled if this mechanism is enabled.

The microcontroller can read and execute instructions

out of the internal ROM program memory, regardless of

the state of the code-protect Configuration bits.

EXAMPLE 3-1:

ROM PROGRAM READ

TABLE 3-1:

REGISTERS ASSOCIATED WITH PROGRAM ROM

Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value on

POR,

BOR

Value on

all other

Resets

10Dh

PMADR

Address Register Low Byte

xxxx xxxx

uuuu uuuu

10Fh

PMADRH

—

Address Register High Byte

xxxx xxxx

uuuu uuuu

10Ch

PMDATA Data Register Low Byte

xxxx xxxx

uuuu uuuu

10Eh

PMDATH

—

Data Register High Byte

xxxx xxxx

uuuu uuuu

18Ch

PMCON1

—(1)

—

1--- ---0

Legend:

= unknown, u = unchanged, r = reserved, – = unimplemented read as ‘0’. Shaded cells are not used during ROM

access.

Note

This bit always reads as a ‘1’.

BSF

STATUS, RP1

;

BCF

STATUS, RP0

; Bank 2

MOVF

ADDRH, W

;

MOVWF

PMADRH

; MSByte of Program Address to read

MOVF

ADDRL, W

;

MOVWF

PMADR

; LSByte of Program Address to read

BSF

STATUS, RP0

; Bank 3 Required

Required

BSF

PMCON1, RD

; ROM Read Sequence

Sequence

NOP

; memory is read in the next two cycles after BSF PMCON1,RD

NOP

;

BCF

STATUS, RP0

; Bank 2

MOVF

PMDATA, W

; W = LSByte of Program PMDATA

MOVF

PMDATH, W

; W = MSByte of Program PMDATA

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