ST STM32F10 Series User Manual

UM0306 Debug support (DBG)
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Note: When the APB bridge write buffer is full, it takes one extra APB cycle when writing the
REMAP_AF register. This is because the deactivation of the JTAGSW pins is done in two
cycles to guarantee a clean level on the nTRST and TCK input signals of the core.
● Cycle 1: the JTAGSW input signals to the core are tied to 1 or 0 (to 1 for nTRST, TDI
and TMS, to 0 for TCK)
● Cycle 2: the GPI/O controller takes the control signals of the SWJTAG I/O pins (like
controls of direction, pull-up/down, Schmitt trigger activation, etc.).
20.4.3 Internal pull-up and pull-down on JTAG pins
It is necessary to ensure that the JTAG input pins are not floating since they are directly
connected to flip-flops to control the debug mode features. Special care must be taken with
the SWCLK/TCK pin which is directly connected to the clock of some of these flip-flops.
To avoid any uncontrolled I/O levels, the STM32F10x embeds internal pull-ups and pull-
downs on JTAG input pins:
● JNTRST: Internal pull-up
● JTDI: Internal pull-up
● JTMS/SWDIO: Internal pull-up
● TCK/SWCLK: Internal pull-down
Once a JTAG I/O is released by the user software, the GPIO controller takes control again.
The reset states of the GPIO control registers put the I/Os in the equivalent state:
● JNTRST: Input pull-up
● JTDI: Input pull-up
● JTMS/SWDIO: Input pull-up
● JTCK/SWCLK: Input pull-down
● JTDO: Input floating
The software can then use these I/Os as standard GPIOs.
Note: The JTAG IEEE standard recommends to add pull-ups on TDI, TMS and nTRST but there is
no special recommendation for TCK. However, for STM32F10x, an integrated pull-down is
used for JTCK.
Having embedded pull-ups and pull-downs removes the need to add external resistors.
SWJ
_
CFG
[2:0]
Available DEBUG ports
SWJ I/O pin assigned
PA13 /
JTMS/
SWDIO
PA14 /
JTCK/
SWCL
K
PA15 /
JTDI
PB3 /
JTDO
PB4/
JNTRS
T
000
Full SWJ (JTAG-DP + SW-DP) - Reset
State
XXXXX
001
Full SWJ (JTAG-DP + SW-DP) but without
JNTRST
XXXX
010 JTAG-DP Disabled and SW-DP Enabled X X
100 JTAG-DP Disabled and SW-DP Disabled Released
other Forbidden
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ST STM32F10 Series Specifications

General

Brand	ST
Model	STM32F10 Series
Category	Microcontrollers
Language	English