User's Manual

RN-42 Specification
7 Design Concerns
7.1 Reset circuit
RN-42 contains a 1k pull up to VCC, the polarity of reset on the RN42 is ACTIVE LOW.
A power on reset circuit with delay is OPTIONAL on the reset pin of the module. It should
only be required if the input power supply has a very slow ramp, or tends to bounce or
have instability on power up. Often a microcontroller or embedded CPU IO is available to
generate reset once power is stable. If not, there are many low cost power supervisor
chips available, such as MCP809, MCP102/121, and Torex XC61F.
7.2 Factory reset PIO4
It is a good idea to connect this pin to a switch, or jumper, or resistor, so it can be
accessed. This pin can be used to reset the module to FACTORY DEFAULTS and is
often critical in situations where the module has been mis-configured. To set Factory
defaults start HIGH, then toggle times.
7.3 Connection status
PIO5 is available to drive an LED, and blinks at various speeds to indicate status.
PIO2 is an output which directly reflects the connection state, it goes HIGH when
connected, and LOW otherwise.
7.4 HCI mode
The RN42 module must be loaded with special firmware to run in HCI mode. When in
HCI mode the standard SPP/DUN applications are disabled.
7.5 Using SPI bus for flash upgrade
While not required, this bus is very useful for configuring advanced
parameters of the Bluetooth modules, and is required for upgrading the firmware on
modules. The suggested ref-design shows a 6pin header which can be implemented to
gain access to this bus. A minimum-mode version could just use the SPI signals (4pins)
and pickup ground and VCC from elsewhere on the design.
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