SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
The serial port backdoor is most useful if the serial port is being used for primary to secondary communication. The serial port (RX) pin can be programmed as an input and its state read. If the line is high, the serial port is in its normal state. If it is low, then the flash should be cleared. It may be necessary to put in a pull up resistor if chip transmitting is absent or powered down. It is also necessary to ensure that the other chip will not transmit data when the UCD3138 is coming out of reset. If this is done, the UART RX pin can be used as a backdoor, and as an RX pin. This mode is used in the UCD3138 introductory lab training programs.
Advantages
Disadvantages