PIC16C925T-SSLASHCL datasheet(30/182 Pages) MICROCHIP

30 / 182 page

PIC16C925/926

DS39544A-page 28

Preliminary

 2001 Microchip Technology Inc.

3.3

Reading the 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 NOP instruction. Therefore, it can be read

as two bytes in the following instructions. The PMDATA

and PMDATH registers will hold this value until another

read operation.

EXAMPLE 3-1:

PROGRAM READ

3.4

Operation During Code Protect

If the program memory is not code protected, the pro-

gram memory control can read anywhere within the

program memory.

If the entire program memory is code protected, the

program memory control can read anywhere within the

program memory.

If only part of the program memory is code protected,

the program memory control can read the unprotected

segment and cannot read the protected segment. The

protected area cannot be read, because it may be

possible to write a downloading routine into the

unprotected segment.

TABLE 3-1:

REGISTERS ASSOCIATED WITH PROGRAM MEMORY

BSF

STATUS, RP1

;

BSF

STATUS, RP0

; Bank 3

MOVLW

MS_PROG_PM_ADDR

;

MOVWF

PMADRH

; MS Byte of Program Address to read

MOVLW

LS_PROG_PM_ADDR

;

MOVWF

PMADR

; LS Byte of Program Address to read

BCF

STATUS, RP0

; Bank 2

BSF

PMCON1, RD

; PM Read

;

; First instruction after BSF PMCON1,RD executes normally

BSF

STATUS, RP0

; Bank 3

;

NOP

; Any instructions here are ignored as program

; memory is read in second cycle after BSF PMCON1,RD

;

MOVF

PMDATA, W

; W = LS Byte of Program PMDATA

MOVF

PMDATH, W

; W = MS Byte of Program PMDATA

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

10Ch

PMCON1

(1)

—

1--- ---0

18Ch

PMDATA

Data Register Low Byte

xxxx xxxx

uuuu uuuu

18Dh

PMADR

Address Register Low Byte

xxxx xxxx

uuuu uuuu

18Eh

PMDATH

—

Data Register High Byte

xxxx xxxx

uuuu uuuu

18Fh

PMADRH

—

Address Register High Byte

xxxx xxxx

uuuu uuuu

Legend: x = unknown, u = unchanged, r = reserved, - = unimplemented, read as '0'.

Shaded cells are not used during FLASH access.

Note 1: This bit always reads as a ‘1’.

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