how many ic's can be connected to 8-bit bus line

[dinesh401]

i am using at89s52 controller port as a output .. from that port i connected to a 8 bit buffer. from the output of buffer ic(74ls573) i want to connect 18 multiplexers(cd4051) ic's which is having the common bus line. is there any problem while connecting this type of circuit.
according to the datasheets, the output current of buffer is 20uA. and the input current of multiplexer is 0.1uA.
if i connect like this, will there any problem?

 

[mister_rf]

I think that fan-out is no longer the main problem here, as in 74LS573 datasheet we find:
High Level Output Current I_OH= -2.6mA and
Low Level Output Current I_OL= 24mA (not the 20uA you have mentioned )

Combining TTL and CMOS technology may present problems when the two types of gates are used in the same system. Sometimes the TTL output voltage levels will not be compatible with CMOS input voltage requirements. According to the standards a TTL logic "1" output signal is between 5 volts and 2.7 volts, but the CMOS gate input level "1" expected between 5 volts and 3.5 volts, so given this mismatch it might not be properly interpreted by.
We can fix this problem by rising the TTL gate's "1" output signal voltage level by means of a pull-up resistor.
Example how to calculate the pull-up resistor here, on pages 19-20:
https://www.ti.com/lit/an/scla007a/scla007a.pdf

 

[HTA]

Beside the DC load it might be needed to look at the capacitive load of the 18 CD4051 input driven by a LS573 output. Depending on the switsching speed needed it could be necessary to use two driver or more. It the bus lines are very long line reflection might be a topic as well.

Enjoy your design work!