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AN247 डेटा पत्रक PDF( Datasheet डाउनलोड )


डेटा पत्रक - A CAN Bootloader - MicroChip

भाग संख्या AN247
समारोह A CAN Bootloader
मैन्युफैक्चरर्स MicroChip 
लोगो MicroChip लोगो 
पूर्व दर्शन
1 Page
		
<?=AN247?> डेटा पत्रक पीडीएफ

AN247 pdf
AN247
Even with careful planning, there may be situations
where safety is actually compromised as a result of bus
contention. In these cases, the best option may be to
put all nodes in the network into a “Configuration” mode
and shut down all system functions.
FIGURE 1:
RX TX
BOOTLOADER FUNCTIONAL
BLOCK DIAGRAM
Bootloader Firmware
Boot Mode Entry
Boot mode entry is determined by an event. This could
be a hardware event, such as pressing one or more
buttons after a device RESET. It could also be a net-
work event, such as a special set of data that tells a
device to enter Boot mode. One example is a network
boot ID that is mapped directly into the CAN ID. Then
the key, along with specific target information, could be
embedded in the data field of a CAN frame. The key
information could put one or more nodes into Boot
mode.
BOOTLOADER FIRMWARE
Basic Operation Overview
CAN
Module
Data
(Msg Identifier)
CONTROL/DATA
Control/Data Buffer
PUT/GET
FLASH
Program
Memory
EE Data
Memory
Configuration
Memory
D8
Bootloader
Control
Registers
D0
Memory I/O
Logic
An overview of the CAN bootloader’s operation is
shown in Figure 1. A CAN Message Identifier and data
is received through the CAN module. One bit in the
identifier is used to indicate whether to PUT or GET
data. Another is used to determine if the message is to
FIGURE 2:
PROGRAM MEMORY MAP OF
THE PIC18F458
be interpreted as data to be programmed or bootloader
control information. Writing data automatically invokes
the appropriate function to write to memory (FLASH,www.DataSheet4U.com
Data EEPROM, or Configuration Memory). Writing to
Boot Program
RESET Vector
0000h
0200h
the Control registers sets the operation of the
bootloader.
High Priority Interrupt Vector 0208h
The bootloader can be configured at build time to sup-
port one of two mutually exclusive modes of operation.
In P Mode (or Put-only) mode, the microcontroller only
accepts PUT commands, and never “talks back” to the
source. In PG Mode, both PUT and GET commands
are accepted, allowing the source to both read from
and write to the target’s memory.
Low Priority Interrupt Vector 0218h
A more detailed explanation is provided in subsequent
sections.
Memory Organization
PROGRAM MEMORY USAGE
Currently, PIC18F devices reserve the first 512 bytes of
Program Memory as the boot block. Future devices
may expand this, depending on application require-
ments for these devices. This bootloader is designed to
occupy the current designated boot block of 512 bytes
(or 256 words) of memory using the recommended
options. Note, however, some compile time options can
grow the bootloader beyond the boot block. Figure 2
shows a memory map of the PIC18F458. The boot
area can be code protected to prevent accidental
overwriting of the boot program.
Program Memory
7FFFh
Note: Memory areas not shown to scale.
DS00247A-page 2
2003 Microchip Technology Inc.

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