Rainbow Electronics RC1090 - Manual (Page 6)

RC1040/1080/1090
 2005 Radiocrafts AS RC1040/RC1080/RC1090 Data Sheet (rev. 1.3) Page 6 of 17
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. This is valid for the RC12x0-series only. For the RC10x0-modules
direct control of the RESET-pin must be used
• 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
reduce the voltage swing due to the internal resistor.