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SR/AI
SR/AP
Hardware Reference
Release r09
Page 24 of 76
3.15 Operating in a Power-Switched Environment
A potential "back feeding" problem may arise, if the module is operated in an environment where
its power supply (VSUP) is switched off by the application. This might be done to save some power
in times Bluetooth is not needed.
As stated in Table 6, the voltage on any I/O pin must not exceed VSUP by more than 0,4V at any
time. Otherwise some current I
INJECT
flows through the internal protection diodes. This may damage
the module.
There is no problem if the application circuit design and programming can assure that all signals
directed towards SR are set to low (U < 0,3V) before and while VSUP is turned off. If this
is not guaranteed, at least a series resistor (about 1k) must be inserted into the signal path. This
does protect the module but obviously cannot prevent from an unwanted, additional current flow in
case of such signal being at high-level. It may be necessary to use driver chips in such appli-
cations, that gate off these signals while VSUP is not present.
3.16 Serial Wire DEBUG Interface
The Serial Wire interface SWDIO, SWCLK is normally not used
in a customer’s product. It is
reserved for debugging purposes.
Leave SWDIO, SWCLK unconnected. Only if you intend to use it for debugging purposes, make it
available and connect SWDIO via a pullup resistor 100k
Ω to VSUP (refer to [1]).
3.17 TRACE Interface
5
The Trace UART TXD interface provides firmware internal trace information and is normally not
used in a customer’s product. In cases where customer support by Stollmann is requested it may
provide useful information about SR internal states and processes while in operation.
We recommend leaving GPIO[6] unconnected but allowing access to the signal (e.g. by routing it
to a via or a header).
5
subject to firmware support, contact Stollmann for current status
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