S42
Hardware User Guide
1VV0301303 Rev. 11
Page 30 of 85
2021-05-06
Not Subject to NDA
•
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 test modes. During the homologation
process, UART-RXD, UART-TXD, UART-RTS# and UART-CTS# must be freely accessible.
3.11.
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 14, 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 5.1 for limits).
There is no problem if the application circuit design and programming can assure that all
signals directed towards S42are 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.
