S42M Hardware User Guide
1VV0301379 Rev. 4
Page
19
of
48
2018-11-28
Test Mode
For regulatory approval purposes, the ability of test mode operation like
“Direct Test Mode”
(DTM) is mandatory. The Direct Test Mode (as defined by the Bluetooth SIG) is part of the
S42M.
For enabling the test mode the S42M provides the Testmode# IO pin. This pin is
low active, connect to GND to activate DTM.
To enter and use DTM, access to the following signals is required:
•
TESTMODE#
•
UART-RXD
•
UART-TXD
•
UART-RTS#
•
UART-CTS#
•
GND
These pins shall be routed to some test pads on an outer layer, but can be left open during
normal operation when not used.
Please note the UART is required for operation of DTM. For any
regulatory approval, UART-RXD, UART-TXD, UART-RTS# and
UART-CTS# must be freely accessible.
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 4, the voltage on any I/O pin must not exceed VSUP by more than 0,3V
at any time. Otherwise, some current I
INJ
flows through the internal protection diodes. This
may damage the module (please refer to chapter 6.1 for limits).
There is no problem if the application circuit design and programming can assure that all
signals directed towards S42M 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 each 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 applications, that gate off these signals while VSUP
is not present.
Summary of Contents for BlueMod+S42M
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