Rainbow Electronics RC2100 - Manual (Page 12)

RC2100
 2005 Radiocrafts AS RC2100 Data Sheet (rev. 1.0) Page 12 of 22
Power Management
The module can be set in SLEEP mode or OFF mode in order to reduce the power
consumption.
The low power SLEEP mode is entered by using the SLEEP command (‘Z’), see RC232™
User Manual, or by pulling both RXEN and TXEN low. In sleep mode the module will not
receive or detect incoming data, neither from the host (UART port) nor from the RF
transceiver. The module is awakened from the SLEEP mode by a positive edge on the
CONFIG (only when ‘Z’-command is used), RXEN or TXEN pins.
Note: If UART handshake is used, the RXEN and TXEN pins can not be used to enter SLEEP
mode. In this case, use the SLEEP command.
The ultra-low power OFF mode is entered by pulling the ON/OFF pin low. The module will
then shut down completely. The module is turned on by setting the ON/OFF pin high (to
VCC). After the module has been in OFF mode all operational parameters are set to the
default values stored in configuration memory.
The VDD output should not be used to supply external circuits, other than for pull-ups for
RXEN, TXEN and CONFIG.
In order to ensure that the internal Power On Reset (POR) operates correctly, the maximum
rise-time specification for VCC must be met (see Electrical Specifications). If longer rise-time
is expected it is recommended to use an external POR circuit attached to the RESET pin (see
Application Note AN001). Slow VCC rise-time or short power interruptions may cause
improper operation that is not handled by the internal POR. In this case the RESET should
be activated in order to ensure proper start-up (see also below).
Important note on using OFF mode:
When turning the module OFF by setting ON/OFF low, great care should be taken to ensure
proper power-on-reset (POR). Three alternatives can be used:
• Control the RESET pin by a separate I/O pin from the MCU using a 100 kOhm series
resistor (RESET does not have any internal serial resistor). Set RESET low before
ON/OFF is turned low, and keep low until ON/OFF is high again (VCC – 10%). This
will ensure proper power-on reset (POR).
• If a dedicated I/O pin for the RESET signal is not available, a 10 kOhm series resistor
from ON/OFF to RESET can be used, and controlling ON/OFF with a 3 / 5V signal
from the MCU.
• Use an external POR and brown-out supervisory circuit. The circuit should be
connected between VDD and GND, controlling RESET. This solution will force
RESET low as long as VDD is below the threshold voltage. The RESET has an
internal pull-up resistor to VDD, thus an open-drain output supervisory circuit can be
used. A threshold voltage of 2.5 V is recommended. Supervisory circuits at 2.5V are
for example MAX803 and MAX6328.
As noted in the Pin Description, RXEN (CTS/RXTX), TXEN (RTS) and CONFIG pins should
have their pull-ups connected to VDD, not VCC. If RXEN is used as CTS (hardware
handshake) or as RXTX (RS485) output, no pull-up is required and should be avoided as this
would reduce the voltage swing due to the internal series resistor.