AN1575
APPLICATION NOTE
ON-BOARD PROGRAMMING METHODS
FOR XFLASH AND HDFLASH ST7 MCUs
by Microcontroller Division Applications
INTRODUCTION
This application note presents various ways of programming a Microcontroller (MCU) that has
already been soldered on a PCB. This “on-board” programming process can be used to up-
date either the whole firmware or only a set of data. The techniques described are fully sup-
ported features of the STMicroelectronics range of MCUs with embedded non-volatile memo-
ries (OTP, then FLASH) designed to meet the needs of equipment manufacturers and cus-
tomers. The ever-growing importance of Surface Mounted Devices (SMD) with high pin count
makes it more and more complex and costly to program with standard programming tools,
while the constraints of time-to-market and flexibility make it necessary to be able to program
or reprogram the products as late as possible in the production cycle, even at the final cus-
tomer site. Aside from these manufacturing considerations, the capability of an MCU to be re-
programmed in-situ opens new application fields: customization, performance upgrades, re-
mote maintenance, etc, are features that are valued by the end-customer.
Two main contexts have to be considered:
– Programming a MCU in the framework of a production line or when the application is not run-
ning (see Section 1).
– Programming the MCU ‘on the fly’ while it is running in the application, generally at the cus-
tomer site (see Section 2).
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ON-BOARD PROGRAMMING METHODS FOR XFLASH AND HDFLASH ST7 MCUs
1 APPLICATION NOT RUNNING DURING PROGRAMMING
This case covers applications that can be stopped during the programming operation: either
because there is no need to keep the application running, or because the programming
process does not require any special firmware to be run by the MCU. This last point means the
application design is compatible with the programming method and tools used.
For this purpose, STMicroelectronics has defined an In Circuit Programming (ICP) method
with a minimum of constraints on the application design.
1.1 ICP OVERVIEW
With this method, the MCU is switched by the programming tool into a special operating mode,
called In Circuit Communication (ICC) mode, by an event sequence on the RESET, VPP/
TEST, ICCCLK and ICCDATA pins: Throughout the entire programming operation, it remains
under control of the programming tool and all transactions go through the ICCCLK and
ICCDATA lines.
In order to be compatible with the ICP method, the application must therefore be equipped
with a special connector for the RESET, VPP/TEST, ICCCLK and ICCDATA signals, while re-
specting some guidelines in order not to interfere with other parts of the application.
Note that this connector features a VPP/TEST line to allow to supply 12V externally on the
VPP pin for HDFLASH-based devices.
When using the ICP method, the user has exactly the same features as on any programming
tool: the whole program memory range, as well as the option bytes can be accessed.
1.2 ICP PRACTICAL IMPLEMENTATION
The ICP implementation is purely a hardware issue as shown in Figure 1. No embedded
firmware needs to be developed. On the other words, the ICP method can be used to program
a blank MCU.
The only sensitive point is sometimes to correctly isolate the RESET, ICCCLK and ICCDATA
in order to avoid any conflict with the devices connected to these pins for purposes of the final
application. This is generally ensured by simple resistors (more details can be found in the
MCU datasheets or in the ST7 ICC Reference Manual).
During the ICP process, the MCU’s embedded peripherals remain in reset state since no soft-
ware is running to activate them. It should be noted however that the hardware watchdog is
disabled.
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ON-BOARD PROGRAMMING METHODS FOR XFLASH AND HDFLASH ST7 MCUs
1.2.1 Application power supply
The application does not need to use its own power supply if the programming tool supplies
power through pin 7 of the ICC connector. This is the case when using STMicroelectronics
programming tools (Refer to the Programming Tool manual).
1.2.2 Application clock
In case the application does not have its own clock during the ICP process (Option byte not
programmed yet,..), the ICC connection can be used to input an external clock from the pro-
gramming tool.
Figure 1. ICP Hardware Design
PROGRAMMING TOOL
ICC CONNECTOR
ICC Cable
APPLICATION BOARD
OPTIONAL
(See text)
ICC CONNECTOR
OPTIONAL
(See text)
9
10
7
8
5
6
3
4
1
2
APPLICATION
RESET SOURCE
Isolation
10kΩ
APPLICATION
POWER SUPPLY
C
L2
C
L1
Isolation
Isolation
RESET
ICCSEL/VPP
ICCDATA
ICCCLK
OSC2
OSC1
V
DD
V
SS
APPLICATION
I/O
ST7
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ON-BOARD PROGRAMMING METHODS FOR XFLASH AND HDFLASH ST7 MCUs
2 APPLICATION RUNNING DURING PROGRAMMING
This method is primarily for applications that cannot be stopped and which have to keep some
kind of software kernel running all the time (generally for security or safety reasons).
It also covers, and this is the most common reason for not using ICP, applications where the
application designer chooses alternative means of implementing the programming process,
specifically:
– The hardware connection to the programming tool, where the new firmware is stored
– The software protocol that defines the commands, status and data format.
A typical case is when a communication port already used in the application is available: It
avoids implementing an additional connector just for the ICP process: this approach is widely
used for devices with a CAN or USB interface.
Using your own protocol for on-board programming has the advantage of allowing flexibility in
terms of hardware implementation. However, some firmware must already be present on the
MCU in order to run the communication protocol: This method can thus be used only for re-
programming, which implies the MCU has been programmed at least once before with an-
other method. Another constraint is that it is not possible to reprogram the whole program
memory of the MCU: nor can the reprogramming firmware itself be altered.
ST7 STMicroelectronics MCUs with HDFLASH and XFLASH have this capability of running
user-specific firmware to perform In-Application Programming (IAP) of the MCU program
memory.
This feature not only allows the application to keep some background tasks running, but also
to allows you to use any type of communication protocol for the reprogramming process.
2.1 IAP OVERVIEW
The ST7 program memory is divided into several (up to 3) sectors. Only Sector 0 cannot be
programmed or erased in normal (user mode) operation. So this sector can be used to exe-
cute the firmware handling the reprogramming process, without being altered.
Reprogramming any of the other sectors is possible, and is based on the execution of a spe-
cific software sequence, for which a software library, the IAP driver, is provided by STMicroe-
lectronics.
The Sector 0 firmware handles the complete protocol and sequencing of the operations, and
some tasks that cannot be stopped during the programming process.
In contrast to the ICP process, the embedded hardware peripherals can be activated by the
Sector 0 firmware to carry out some background tasks. The only limitation is that the Interrupt
Requests coming from these peripherals (Reception on UART, Timer overflow, ..) can be
processed only after the IAP driver has completed the requested operations. A notable excep-
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ON-BOARD PROGRAMMING METHODS FOR XFLASH AND HDFLASH ST7 MCUs
tion is the hardware watchdog that remains active: It must therefore be refreshed before per-
forming any Program/Erase operations on the FLASH.
2.2 IAP PRACTICAL IMPLEMENTATION
2.2.1 General architecture
As already stated, a firmware must already have been loaded into Sector 0. This firmware has
three purposes:
– Performing the Erase/Write operations on Sector 1 or 2 of program memory.
– Receiving the new data to be programmed.
– Managing the whole process protocol (Commands and status).
Therefore the firmware contained in the Sector 0 is generally based on three modules: Pro-
tocol layer, Data Transfer Layer and IAP Driver (Figure 2)
Figure 2. IAP Architecture
Software architecture
Commands
Data Flow
Protocol Layer
New Data
Status
Data Transfer Layer
MCU RAM
IAP Driver
MCU FLASH
This chart only gives the generic scheme of an IAP application, however the various types of
New Data
sources,
Data Transfer
physical supports, and the
Protocol Layer
interfaces can
lead to a wide range of practical implementations.
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