Greetings,
I need some help.
I'm building a display using serial port for it's data source. It is a 2 digit display utilizing 89S51 and 74LS247. I'm attaching the schematics. Before proceeding to producing the PCB, I built a basic system, just the 89S51 and 74LS247, without it's serial port (I only use the components in the blue rectangle.



Thank you Andy Neil for your hints ...
Thank you Michael Karas for your guidance ...

Then I downloaded my testing program, like this :

MULAI:
MOV P2,#8AH;
JMP MULAI;

What happened next is quite confusing for me.
I can not get the result from port 2 as what I wrote in the program.
When I plug in the power, the result is not always the same. I keeps on changing from one trial to another.
I checked the supply voltage, it's at 4.99 - 5.01 Vdc.

Could anyone enlight me to which part that I messed up? (Possibly some points all together)

Thank you in advance for your help.