General description
UM0527
20/66
The interface unit provides the connection from the UPS unit to the PC via RS, USB or joint
signals. The interface contains a USB to RS232 converter based on the microcontroller
ST72F623F2M1, in the SO20 package powered from the PC, with optoisolation barrier
(PC817B) and RS232 with optoisolation barrier (PC817B). The required voltage for the
RS232 circuits is realized by the voltage pump converter built with NE555. The interface unit
also contains an analog multi/demultiplexer M74HC4053 used to switch signals from the
USB and RS232 to the microcontroller.