Hello Mohit!

1. 8031 with bus drivers (i. g. 74HCT245)

There are two control pins on the 245, DIR and /OE. DIR controls the data flow through the driver, /OE enables its output.

Data flows into the microcontroller, coming from the EPROM (when /PSEN is low) or coming from the RAM (when /RD is low). Data comes out of the microcontroller and flows to the RAM when /WR is low. Don't forget - like I did first time - that data even flows out of the microcontroller in its adress multipexing bus cycle: A0-A7 comes out on the AD0-AD7 pins and is latched in the adress latch (i. g. 74HCT573)!

So you may test the following: connect the B side of the driver to the AD0-AD7 pins of the microcontroller and the A side to the memory. Connect DIR to /WR and ALE to /OE. This should work.

If you want to buffer the A8-A15 adress lines, there are wether multiplexing nor read cycles so you can connect the control lines of the driver to to the supply voltage and to ground.

Buffering the lower adress lines don't make sense because of the buffering capabilities of the adress latch.

2. Pull up resistors

In Port 0 of an 8031 the output stage is realized by only by pull down transistors. So if you want to achive H levels on its lines you have to use pull up resistors - theoretically, but not practically: in one of the clock cycles a strong internal pull up resistor is connected for a short time between the supply voltage and the output pin.

The reason for this is the capacity of input pins wich can be connected to the output pin of the microcontroller: you have to charge them to achive a H level. Because this has to happen in a very small time, the charging current has to be great and so the value of the resistor between the supply voltage and the output pin has to be small.

If this resistor would be connected always, there always would flow a great current trough it, wich is avoided if you connet it just for a little time.

So in practice, I design my PCBs with a SIL pullup resistor at port 0, but I do not use it...

Yours sincerely, MiKe