AN247 datasheet(5/32 Pages) MICROCHIP

5 / 32 page

 2003 Microchip Technology Inc.

DS00247A-page 5

AN247

Command and Data

There are four commands defined to add functionality

and reliability to the bootloader. These are summarized

in Table 2. They are:

• NOP: No operation. This is supplied to allow

writing Control registers without issuing a

command.

• RESET: Reset the device via the RESET

instruction.

• INIT_CHK: Initialize the checksum and verify reg-

isters. This clears the internal 16-bit checksum

and clears the verify flags.

• CHK_RUN: Test the checksum and verify registers;

if valid, then clear the last location of EEPROM.

Data is passed through the Data registers in the

Control register set and added to the checksum;

the program checks for zero. The internal

self-verify flag is also tested for zero.

Note that these are not the only commands that may be

implemented. Users may expand on this basic set by

using the high order bits of register D4, or using combi-

nations of bits to define an expanded command set.

Registers D5 through D7 may also be used to define

additional parameters in combination with commands.

The basic 8-register structure for control allows users

to expand the command sets to their own needs.

TABLE 2:

SUMMARY OF SPECIAL COMMANDS (COMMAND REGISTER D5)

BOOTLOADER DETAILS

Reading/Writing/Erasing Program

Memory

For writing to FLASH Program Memory, the Control

to 2FFFFFh. Read operations occur at the byte level.

Write operations are performed on multiples of 8 bytes

(one block), while erase operations are performed on

64 bytes (one row).

Writing is an immediate operation. When the PUT

“DATA” command is received, the address already

stored in the Control registers is decoded and the data

is written to the target’s Program Memory. Data is only

written if the write operation has been unlocked.

When writing Program Memory, the memory should be

erased first. Either the auto erase or erase only options

can be used to erase memory on every 64-byte border.

The default operation is that bits can only be cleared

when written to. An erase operation is the only action

that can be used to set bits in Program Memory. Thus,

if the bootloader protection bits are not set up in the

Configuration registers, operations on memory from

000h to 1FFh could partially or completely disable the

bootloader firmware.

User IDs (starting at address 200000h) are considered

to be part of Program Memory and are written and

erased like normal FLASH Program Memory.

Reading/Writing EEPROM Data Memory

For writing to EEPROM Data Memory, the Control reg-

ister address must point to memory region F00000h to

FFFFFFh. Read and write operations occur at the byte

level. Write operations must be unlocked before any

write operation can take place.

Note that the last location of the Data Memory is used

as a boot flag. Writing anything other than FFh to the

last location indicates normal code execution.

Configuration Bits

PIC18F devices allow access to the device configura-

tion bits (addresses starting at 300000h) during normal

operation. In the bootloader, the Control register

address must point to memory region 300000h to

3FFFFFh to provide Configuration Memory access.

Data is read one byte at a time and, unlike Program

Memory, is written one byte at a time. Since configura-

tion bits are automatically erased before being written,

the erase control bit will have no affect on Configuration

Memory.

Having access to configuration settings is very power-

ful; it is also potentially very dangerous. For example,

assume that the system is designed to run in HS mode

with a 20 MHz crystal. If the bootloader changes the

oscillator setting to LP mode, the system will cease to

function - including the bootloader! Basically, the

system has been killed by improperly changing one bit.

Command

Code

Description

NOP

00h

No operation.

RESET

01h

Issue a Software Reset to the device.

INIT_CHK

02h

Initialize internal checksum and verify registers.

CHK_RUN

03h

Test the checksum and verify, then clear the last location of EEPROM if valid.

All other commands

04h - FFh Undefined - operate as NOP.

AN247 Datasheet(PDF) 5 Page - Microchip Technology

AN247 Datasheet(HTML) 5 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL