ST AN2260 Application note

AN2260

APPLICATION NOTE

STR73x SystemMemory Boot Mode

Introduction

This application note describes the features of the SystemMemory boot mode developed for STR73x
Flash microcontrollers to provide all the basic functionality to support programming of the embedded
Flash. It will describe its general features, and then move on to specific features of the UART boot mode.

Rev 1

November 2005 1/10

www.st.com

10

AN2260

Contents

1 General description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Entering SystemMemory boot mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Hardware requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3 Loading code in SystemMemory boot mode . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4 Exiting SystemMemory boot mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5 SystemMemory code program flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 UART SystemMemory boot mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1 UART SystemMemory code sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2 Choosing the UART baud rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2.1 Minimum baud rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2.2 Maximum baud rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2.3 Higher baud rate deviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2/10

AN2260 1 General description

1 General description

The STR73x is normally woken up in SystemMemory boot Mode when the Flash is still not
programmed in the manufacturing line environment. In this case the system boot is performed
from SystemMemory sector in the Flash bank0. This mode allows initializing the Flash
programming via a serial interface. The SystemMemory code is going to load a Flash
programming code (called “loader” from now on) into internal RAM via the UART0 serial
interface.

1.1 Entering SystemMemory boot mode

The STR73x enters the SystemMemory Boot Mode if the mode pins are configured with M0=0,
M1=1 as the hardware reset pin (RSTIN) transitions High at the end of a hardware reset. The
M1 signal is used to stretch the internal clock. M1 must be forced back to Low (0) after the
RSTIN pin has stabilized. Forcing M1 Low is required in order to enable propagation of the
system clock throughout the device.

As the M1 pin is forced Low the STR73x CPU begins executing the SystemMemory code which
resides in the SystemMemory Sector now mapped at address 0x00000000.

Note: The normal Flash boot sector will not be available at address 0x00000000 until the

SystemMemory sector is re-mapped to 0x8010C000 by clearing the SMBM bit in the Flash
Control Register 0. The SystemMemory code does not perform this re-mapping operation.

Table 1. STR73x device configuration in SystemMemory Boot Mode

Feature/Peripheral State Comment

Instruction Set THUMB Save code space with 16-bit instructions

CPU Mode Supervisor Full access with IRQ/FIQs disabled

Input Clock External Quartz allow a Frequency in a range of 4 to 8MHz

CLK2 Div2 Enabled -

Free running

PLL

UART0_RX Pin Input UART0 receive

UART0_TX Pin Default Only configured for UART Boot

UART0 Registers Default Only configured for UART Boot

MX=12

DX=2

System Clock in a range of 12 to 24MHz to enable

higher serial link baudrates

1.2 Hardware requirements

The hardware required for putting the STR73x into SystemMemory boot mode would consist of
any circuitry, switch, or jumper capable of holding the M1 pin High during Reset, and then
forcing M1 Low after the reset is complete. For more details refer to the application note
STR73x Hardware Getting Started (AN2156), Boot Management section.

To connect to the STR73x during SystemMemory boot mode, a RS232 serial interface must be
directly linked to UART0 pins, for more details refer to the AN2156 document.

3/10