1 General description

AN2260

4/10

Note:

The serial link receive interface pin (UART0_RX) must be held HIGH during the

SystemMemory code initialization phase.

1.3

Loading code in SystemMemory boot mode

As previously described, the STR73x enters SystemMemory boot mode by controlling the state

of the M1 pin during the Reset Sequence.

Following the serial link initialization sequence (see the following chapters) the SystemMemory

code enters a loop to receive a specified number of bytes, and store them sequentially to RAM

starting at address 0xA0000000. The receive byte count depends on the serial interface and is

currently defined as 128 bytes for UART.

When the proper number of bytes is received, the STR73x then jumps to address 0xA0000000

and begins to execute the downloaded code.

Generally, this small piece of code (called loader or monitor) will contain another receive loop

which may then continue to load code and data at a user specified location. The pre-initialized

serial link may be used accomplish this without modifications.

The second level of downloaded code may contain the final user application. It may also

contain another, more sophisticated, loader routine which adds a transmission protocol to

enhance data integrity. The secondary loader may even change to a different download

method, baud rate, system operating frequency, etc.

1.4

Exiting SystemMemory boot mode

SystemMemory boot mode must be terminated in order to execute a program in a normal

USER mode. The STR73x may exit this mode by applying a hardware Reset on the RSTIN pin.

At the time of the reset, the mode pins (M0 & M1) must be set at the proper levels to enter the

desired user mode. Following the reset, the STR73x CPU will begin executing code from

location 0x00000000 of the embedded Flash.

Table 2.

Mode Pin vs Memory Mapping

M1

M0

Boot Mode

Memory Mapping

Note

0

0

User Boot mode 1 FLASH sector B0F0 mapped at 0h

All FLASH sectors accessible

except SystemMemory sector

0

1

User Boot mode 2 FLASH sector B0F0 mapped at 0h

FLASH B0F1 sector and

SystemMemory sector not

accessible

1

0

SystemMemory

SystemMemory mapped at 0h

-

11

Reserved

-

-