UM220-IV L User Manual
UC-00-M15 EN R1.4
Hardware Design
21
4.3
UART
The two serial ports of UM220-IV L are LVTTL levels, which need to be converted
through RS232 level if connected to PC.
UM220-IV L
PC
RS232
Converter
UART2
UART1
RS232 2
RS232 1
Figure 4- 8 Connect to PC through UART
It is recommended that users reserve a test point for serial port 2 as the debug port.
If there is data input on the module input ports (RXD, GPIO) when the module is not powered on, it
will form power leakage on the module VCC. When the leakage voltage is higher than 1.6V, it may
cause a start failure when the module is powered on. To prevent the leakage power, ensure that the
IO port connected to the module is in high impedance or low level when the module is not powered
on.
4.4
RESET Time Sequence
There is a reset chip inside the module. When VCC is lower than 2.63V (typical value of
ambient temperature) or nRESET is at low level, the module is in reset state. After VCC
rises to 2.63V or nRESET changes from low to high, the reset state of the chip will continue
to remain for 200ms.
It is recommended to keep the reset signal of the nRESET pin for 10ms after VCC is valid
at power-up. During normal operation, the minimum valid time of the reset signal for the
nRESET pin is 500ns.
4.5
TIME PULSE Output
The period of the TIME PULSE output signal is 1s, the peak-to-peak value is VCC, and
the default duty cycle is 10%.
