User's Manual

BT900-Sx Hardware Integration Guide
Intelligent BTv4.0 Dual Mode Module
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31 CONN-HIG-BT900
 nAutoRUN pin and operating mode selection
nAutoRUN pin needs to be externally held high or low to select between the two BT900
operating modes at power-up:
- Self-contained Run mode (nAutoRUN pin held at 0V).
- Interactive / development mode (nAutoRUN pin held at VCC).
Make provision to allow operation in the required mode. Add jumper to allow nAutoRUN pin
to be held high or low (via 10K resistor) OR driven by host GPIO.
 I2C
It is essential to remember that pull-up resistors on both I2C_SCL and I2C_SDA lines are not
provided in the BT900 module and MUST be provided external to the module as per I2C
standard.
 SPI
Implement SPI chip select using any unused SIO pin within your smartBASIC application
script then SPI_CS is controlled from smartBASIC application allowing multi-dropping.
 SIO pin direction
BT900 modules shipped from production with smart BASIC runtime engine FW, all SIO pins
(with “default function” of “DIO”) are mostly digital inputs (see Pin Definitions Table2).
Remember to change the direction SIO pin (in your smart BASIC application script) if that
particular pin is wired to a device that expects to be driven by the BT900 SIO pin configured
as an output. Also these SIO pins that are inputs have by default (in FW) no internal pull-up
(TBD) resistor-enabled, and therefore are floating (TBD). You are free to configure in your
smartBASIC application script.
Note: Internal pull-up, pull down will take current from VCC.
 SIO_TBD pin and Over the Air smartBASIC application download feature
SIO_TBD is an input, set with internal pull-down (in FW). Refer to latest FW release
documentation on how SIO_TBD is used for Over the Air smartBASIC application download
feature. SIO_TBD pin has to be pulled high externally to enable the feature. Decide if this
feature is required in production.
 nRESET pin (active low)
Hardware reset. Wire out to push button or drive by host.
By default module is out of reset when power applied to VCC pin.
6.2 PCB Layout on Host PCB - General
Checklist (for PCB):
 MUST locate BT900-Sx module close to the edge of PCB (mandatory for BT900-SA for
on-board chips antenna to radiate properly).
 Use solid GND plane on inner layer (for best EMC and RF performance).
 All module GND pins MUST be connected to host PCB GND.
 Place GND vias close to module GND pads as possible
 Unused PCB area on surface layer can flooded with copper but place GND vias regularly
to connect copper flood to inner GND plane. If GND flood copper underside the module
then connect with GND vias to inner GND plane.
 Route traces to avoid noise being picked up on VCC supply and AIN(analogue) and SIO
(digital) traces.
 Do NOT run any track near pin34 of BT900-Sx. Pin34 is BT_Ext_DS_CLK which the external
supplied 32.768kHz oscillator is connected to. MUST ensure the 32.768kHz is shield by GND
on either side, see devboard PCB layout DVK-BT900-V01.
 Ensure no exposed copper underside of the module (refer to land pattern of BT900
development board).