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Single wire interface module (SWIM) and debug module (DM)

Single wire interface module (SWIM) and debug

module (DM)

5.1

SWIM and DM introduction

In-circuit debugging mode or in-circuit programming mode are managed through a single

wire hardware interface featuring ultrafast memory programming. Coupled with an in-circuit

debugging module, it also offers a non-intrusive emulation mode, making the in-circuit

debugger extremely powerful, close in performance to a full-featured emulator.

5.2

SWIM main features

•

Based on an asynchronous, high sink (8 mA), open-drain, bidirectional communication.

•

Allows reading or writing any part of memory space.

•

Access to CPU registers (A, X, Y, CC, SP). They are memory mapped for read or write

access.

•

Non intrusive read/write on the fly to the RAM and peripheral registers.

•

Device reset capability with status flag in the Reset status register (RST_SR).

•

Clock speed selectable in the SWIM clock control register (CLK_SWIMCCR).

SWIM pin can be used as a standard I/O with some restrictions if you also want to use it for

debug. The most secure way is to provide on the PCB a strap option.

Figure 12. SWIM pin connection

5.3

SWIM modes

After a power-on reset, the SWIM is reset and enters OFF mode.

OFF: Default state after power-on reset. The SWIM pin cannot be used by the

application as an I/O.

I/O: This state is entered by software writing to the SWD bit in the Global configuration

standard I/O pin. In case of a reset, the SWIM goes back to OFF mode.

SWIM: This state is entered when a specific sequence is performed on the SWIM pin.

In this state, the SWIM pin is used by the host tool to control the STM8 with 3

commands (SRST system reset, ROTF read on the fly, WOTF write on the fly).

Note:

Refer to the STM8 SWIM communication Protocol and Debug Module User Manual for a

description of the SWIM and Debug module (DM) registers.

MSv17035V1

MCU

SWIM/PA0

I/O for application

SWIM interface for tools

Jumper selection for

debug process

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