PIC24FXXKA2XX

DS39991A-page 18

 2010 Microchip Technology Inc.

3.8

Reading Code Memory

To read the code memory, execute a series of TBLRD

instructions and clock out the data using the REGOUT

command.

Table 3-9 provides the ICSP programming details for

reading code memory. In Step 1, the Reset vector is

exited. In Step 2, the 24-bit starting source address for

reading is loaded into the TBLPAG register and the W6

register. The upper byte of the starting source address

is stored in TBLPAG, and the lower 16 bits of the source

address are stored in W6.

To minimize the reading time, the packed instruction

word format, which was used for writing, is also used

for reading (see Figure 3-7). In Step 3, the Write

Pointer, W7, is initialized. In Step 4, two instruction

words are read from code memory, and clocked out of

the device through the VISI register, using the REGOUT

command. Step 4 is repeated until the required amount

of code memory is read.

TABLE 3-9:

SERIAL INSTRUCTION EXECUTION FOR READING CODE MEMORY

Command

(Binary)

Data

(Hex)

Description

Step 1: Exit Reset vector.

0000

0000

0000

000000

040200

000000

NOP

GOTO

0x200

NOP

Step 2: Initialize TBLPAG and the Read Pointer (W6) for TBLRD instruction.

0000

0000

0000

200xx0

880190

2xxxx6

MOV

#<SourceAddress23:16>, W0

MOV

W0, TBLPAG

MOV

#<SourceAddress15:0>, W6

Step 3: Initialize the Write Pointer (W7) to point to the VISI register.

0000

0000

207847

000000

MOV

#VISI, W7

NOP

Step 4: Read and clock out the contents of the next two locations of code memory through the VISI register using

the REGOUT command.

0000

0000

0000

0001

0000

0000

0000

0000

0000

0000

0000

0001

0000

0000

0000

0000

0001

0000

BA1B96

000000

000000

<VISI>

000000

BADBB6

000000

000000

BAD3D6

000000

000000

<VISI>

000000

BA0BB6

000000

000000

<VISI>

000000

TBLRDL

[W6], [W7]

NOP

NOP

Clock out contents of VISI register.

NOP

TBLRDH

[W6++], [W7]

NOP

NOP

TBLRDH.B

[++W6], [W7--]

NOP

NOP

Clock out contents of VISI register.

NOP

TBLRDL

[W6++], [W7]

NOP

NOP

Clock out contents of VISI register.

NOP

Step 5: Reset device internal PC.

0000

0000

040200

000000

GOTO

0x200

NOP

Step 6: Repeat Steps 4 and 5 until the required code memory is read.