Oleg Sergeev wrote:
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after some minutes looking at the new schematic yet another notes:

- replace 74HC373 with 74HC573: they are the same but have better pinout;
- 74HC138 has three C inputs: /C3, /C2 and C1 (last one is high-level enable input). Check if they are connected correctly;
- some LCD backlights based on LED, sink current above 100mA. So please check datasheet for this parameter.
I recommend you to use ULN2003/2803 after 373; these chips are open-drain ones prepared to control lamps, relays, etc.

Finally, take my another suggestion which frees one more pin (here: P1.6):

- replace upper 74HC373 with 74HC574;
- connect its strobe input (pin 11) to either /Y2 or /Y3.
This way:
- you save P1.6;
- you may not use external pullup resistor and write to 74HC574 just via MOVX like you do for RAMs. That`s quick and easy!

Regards,
Oleg
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Hi Oleg,

- 74HC373 replaced with 74HC573.

-The '138' features three enable inputs: two active LOW (E1 and E2) and one active HIGH (E3). Every output will be HIGH unless E1 and E2 are LOW and E3 is HIGH. Yes you are right. This is taken care.

- For backlight, a transistor is used.

- all the necessary precautions will be taken to drive relays buzzers etc...

And your suggestion for saving one more port pin was really coooooooool.
I'll implement the code as you have suggested. :-)

Regards
Raj Shetgar