C509-L_97 Datasheet, PDF (246/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Bootstrap Loader
C509-L
10.3 Phase II: Automatic Serial Synchronization with the Host
When the bootstrap loader leaves phase I and enters phase II, the synchronization procedure
between MCU and host will be started. The synchronization must be handled by the host system as
shown in figure 10-6.
Figure 10-6
The Synchronization between MCU and Host
After receiving the testbyte from the host, the bootstrap loader calculates the actual baud rate and
activates the baud rate generator of the serial interface 0. When the synchronization is
accomplished, the MCU sends an acknowledge byte (55H) back to the host. The baud rate
calculation works correctly only in a specific range of baud rates. If the synchronization fails, the
baud rates between MCU and host are different, and the acknowledge code from the MCU can't be
received properly by the host. In this case, the host software may give a message to the customer,
e.g. that he has to repeat the synchronization procedure.
Attention: the bootstrap loader doesn't recognize, if the synchronization was correct. It always
enters phase III after sending the acknowledge byte. Therefore, if synchronization fails, a reset of
the MCU has to be invoked, to restart the bootstrap loader for a new synchronization attempt.
Semiconductor Group
10-8
1997-10-01