ScanTool STN Bootloader - Manual (Page 5)

STN Bootloader
CRC is calculated on the data field prior to byte
stuffing. It is transmitted after the data field, and before
the <ETX> control character.
After a response is received, it must first be
unstuffed. Then the CRC is calculated over the entire
data packet (including the CRC bytes). If the reception
is successful, the CRC calculation result will equal
zero.
4.5 Commands
The data field of each packet transmitted to the
bootloader should contain one command and
(optionally) its associated data. Commands must be
transmitted to the bootloader in the following format:
<command><data length>[<data>]
Table 3 details the command format. Commands
supported by the bootloader are detailed in section 5.0
“Bootloader Commands”.
Table 3 – Command Format
Field
Length
(bytes)
Description
<command> 1 Bootloader command
<data length> 2
Length of command
payload
[<data>] variable
Optional command
payload
Bytes comprising a command do not have to be
sent back-to-back. However, there cannot be more
than 200 milliseconds between any two bytes. If this
timeout occurs, the bootloader will abort receiving the
command, and will revert to looking for the start of the
next command packet.
4.6 Responses
The data field of each packet received from the
bootloader contains one response and its associated
data. The responses are transmitted by the bootloader
in the following format:
<ACK/NACK><command><data length>[<data>]
Table 4 details the response format.
Table 4 – Response Format
Field Length Description
<ACK/NACK> 2 bits
Success/error indication:
01
= ACK
10 = NACK
<command> 6 bits
Command which this
response is
acknowledging
<data length> 1 byte
Length of response
payload
[<data>] variable
Optional response
payload
4.6.1 ACK Responses
Upon successful execution of each command, the
bootloader responds with an ACK response in the
following format:
<0x40|command><data length>[<data>]
See section 5.0 “Bootloader Commands” for details
on responses to each bootloader command.
4.6.2 NACK Responses
When the bootloader encounters an error while
processing a command, it will respond with a NACK
response. NACK responses have a fixed length of
three bytes (one data byte) and are in the following
format:
<0x80|command><0x01><error code>
Table 5 lists possible error codes.
Table 5 – Error Codes
Error Type
Error
Code
(hex)
Description
01 CRC error
Communication
02 Received packet too long
10 Unknown command Command
Validation
11 Invalid command format
30 Sequence error
50 Authentication error
80 Programming error
Firmware
Upload
90 Verification error
4.6.2.1 Communication Errors
NACK responses indicating communication errors
have their command field set to 0x00, because the
integrity of the packet has been compromised or could
not be verified, and the byte received in place of the
command field may not correspond to the command
actually sent by the host. These errors may occur for
any bootloader command. The following two errors
indicate communication problems:
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