6-bit dynamic display circuit

Shown is a typical 6-bit dynamic display circuit .
    In the figure, the PA terminal of 8255 is used to output the display code. PB port output bit selection code. Assume that the display buffer is DISBUF, then
after completing the initialization of 8255, take out the number to be displayed (hexadecimal), use the software decoding method to find the 7-segment control display
code j corresponding to the number to be displayed, and then use the team port The output is amplified by the 74LS07 driver and sent to the data bus of each display. Which digit
is displayed on the digital tube mainly depends on the bit selection code. Only when the line corresponding to the bit selection signal PB port turns to low level after passing through the driver, the corresponding bit will light up
and display. If the digits are displayed in sequence from left to right, each digital tube displays continuously for a period of time (such as Ims), and after the last digit is displayed,
the above process is repeated. In this way, what the human eye sees is 6 digits "simultaneously" show. Among them, 74LS07 is a 6-bit driver, which provides
a certain driving current for LED. Since one 74LS07 only has 6 drivers, the 7-segment digital tube needs two 74LS07s to drive:
the PB port of 8255 is inverted by the 75452 buffer/driver and used as a bit selection signal. A 75452 contains two buffers/drivers, each
with two inputs. Three 75452s are needed to drive a 6-digit digital tube display.