XC886/888CLM
Bootstrap Loader
User’s Manual
18-17
V1.3, 2010-02
Bootstrap Loader, V1.0
•
Protected Identifier (ID) field (3C
H
or 7D
H
)
The Break is used to indicate the beginning of a new frame and it must be at least 13 bits
of dominant value. When a negative transition is detected at pin T2EX at the beginning
of Break, the Timer 2 External Start Enable bit (T2MOD.T2RHEN) is set. This will then
automatically start Timer 2 at the next negative transition of pin T2EX. Finally, the End
of SYN Byte Flag (FDCON.EOFSYN) is polled. When this flag is set, Timer 2 is stopped.
The time taken for the transfer (8 bits) is captured in the T2 Reload/Capture register
(RC2H/L). Then the LIN BSL routine calculates the actual baud rate, sets the PRE and
BG values and activates the Baud Rate Generator. The baud rate detection for LIN is
shown in
Figure 18-2
LIN Auto Baud Rate Detection for Header LIN Frame
18.1.3.1
Communication Structure
The transfer between the PC host and the microcontroller for the 3 phases is shown in
shows the Master Request Header, Slave Response
Header, Command and Response LIN frames.
00
01
02
03
04
Captured Value (8 bits)
SYN BREAK
SYN CHAR (55
H
)
Start
Bit
Stop
Bit
1st negative transition,
set T2RHEN bit
T2 automatically
starts
EOFSYN bit is set,
T2 is stopped
Last captured value of T2
upon negative transition
*