8088 based very basic project question (10+3 points)

Hi, Im working on an 8088 based sine wave generator (variable freq.)


Uptill now I have connected one 8255 PPI (IO/M of 8088 connected to it's CS through an inverter),a 74LS373 (for demultiplexing the address bus)...an 8284 with 10 Mhz crystal. and a 27512 ROM 16 address lines and 8 datalines...

All this is currently connected on a breadboard.

I am getting the clock at 3.333 MHz (as expected) and ALE pulses at 833.3 khz (as expected), but I can't get the O/P on 8255's ports...

AD0 and AD1 of 8088 is connected (through address latch '373) to 8255... I am giving it the 80h as the control word and setting up some o/p values for the ports but nothing seems to work.

I tried include a WAIT statement to check if the processor tested the TEST pin..but it isn't, so i suspect it is not reading from the ROM at all.

I've placed a FAR JUMP (EA 0000 2000) at FFF0 of my ROM to the address where the program resides.


Also, is it required to BUFFER the data bus of 8088?...

I'll donate +10(+3) points to the one who can actually help me out....Thanks a lot.

Has the board run any code so far? I mean, is the issue just the 8255 or you just don't know if the board runs at all?

never used an 8088 but can you answer the following?

do any of your data lines toggle? can you check with a scope?
have you a LS373 for the 0-7 address lines for the ROM and
RAM in your system as well as 8255?

does any of your code work?
can you toggle a buffered LED on unused address space?

is READY line high?
is RESET line high?

are you using direct port instructions or variable output instructions?

are mode and port addresses correct?
mode 0x03
portA 0x00
portB 0x01
portC 0x02

your LS373 output needs to be always enabled (pin1 LOW)

according to the data sheet - data bus does not require buffer.

hope this helps Polymath

thanks for replying guys, but i got it to work by myself. Can't exactly tell you how b/c some of my class mates (competitors) are also present on this board!!!!

Provide Pull up resistor on Address Data Bus..