Hi

I am A.Srirangakumar,from Hyderabad,India.I have interfaced SST89C58 with
1.A RTC (DS12c887)
2.A 128K X 8 bytes NVSRAM (DS1245y)
3.A 20ch X 2 LCD
4.A Printer(parallel)
5.A PC-AT Keyboard.

This is weighing intelligent terminal, which is working in various places in India

I am using normal address de-multiplexing logic.i.e.,using 74LS373
For generating chip select to the peripherals, I am using a 2 to 4 decoder i.e,74LS139.

For addressing the 128K RAM, I have used Pin-1,(For A16 pin).Inputs for decoder are pin-2 and pin-3 as A17 & A18.(Here kindly let me know the address pin assigned is right or wrong)

I am able to address, I mean read as well as write the data that is entered through Keyboard. Even I am able to see the data on LCD duely converting it into ASCII.

For Printer, I have used 74LS374-a octal Flip-flop(like 74ls373).For this I have generated a chip select also.I am even reading the various signals such as Paper out, Error, Online etc, for printer operation.
I am able to print the data on to paper (ofcourse converting it to ASCII and sending character by character).But here my problem is in some places, printer is printing some junk characters or some lines.(Junk characters I mean extended ASCII and ASCII other than alpha-numerals).May I know what may be the cause for this mal-functioning.

Some times, my NVRAM also gets automatically disabled from read or write operations.I am even getting some junk displayed on LCD.

I would like to know any solutions for my above problems

Thanks