C509-L_97 Datasheet, PDF (241/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Bootstrap Loader
C509-L
The serial transfer operates in asynchronous mode with the serial parameters 8N2 (eight data bits,
no parity and two stop bits). The baud rate however can be varied by the host in a wide range,
because the bootstrap loader does an automatic synchronization in phase II.
The bootstrap loader itself does not use any of the implemented interrupts of the MCU for its work.
But for further custom program execution in the bootstrap mode two interrupts are supported. These
are the interrupts for the timer 0 (TIMER0) and for the serial interface 0 (SINT0). As the interrupt
vectors are located in the address area of the bootstrap loader (0000H - 01FFH), the appropriate
interrupt vector addresses are routed by the bootstrap loader via a LJMP instruction to a reserved
XRAM area at F400H - F41FH as shown below:
TIMER0:
SINT0:
usually at 000BH is routed to F400H in XRAM
usually at 0023H is routed to F410H in XRAM
At these addresses (F400H - F40FH and F410H - F41FH) the user specified interrupt routines can
be loaded to handle the interrupts in a user defined way. To avoid unexpected software behavior
when these interrupts are used, the reserved memory area should be used only by interrupt
handling routines. Notice: In this case the XRAM for custom programs is reduced to F420H -
FFFFH. If there is no need of these interrupts, the reserved memory area can be programmed with
custom software.
It is recommended not to activate other interrupts than TIMER0 and SINT0, because this could lead
to uncontrolled software execution in the interrupt vector area (0000H - 0100H)!
10.2 Phase I: Check for Existing Custom Software in the External FLASH Memory
The first action of the bootstrap trap loader is to check two blocks in the external FLASH memory for
the existence of custom software. If the check is successful, the custom software is started directly.
If no software is found, phase II is entered to establish a serial communication with the connected
host. This feature can be used to protect the external FLASH memory contents against
unauthorized in-system reading and writing in the bootstrap mode. The security check can be used
if needed, but can also be skipped as well, as described in the next section.
10.2.1 Custom Software Check by the Info Block
For the above mentioned custom software two memory sectors (sector A: at C000H, sector B: at
6000H) of the external FLASH memory are reserved. For activation of the FLASH memory check,
an info block is required, which has to be written at the beginning of the corresponding external
FLASH memory sector. The structure of the info block is shown in figure 10-3.
The sector addresses C000H and 6000H are valid for the C509-L devices with stepping code CA
and later.
Semiconductor Group
10-3
1997-10-01