interfacing MAX1232 to at89c2051?

Have you read the datasheet for the MAX1232?

It contains _very clear_ instructions how to connect the chip electrically, and how to interact with it in software.

All you need to do, is learn how to toggle a digital output for the watchdog (brownout level and watchdog timeout length is normally hard-coded by holding the pins high or low), and then make sure that you perform the port toggling often enough.

As a power monitor:

A voltage detector monitors VCC and holds the reset
outputs (RST and RST) in their active states whenever
VCC is below the selected 5% or 10% tolerance (4.62V
or 4.37V, typically). To select the 5% level, connect
TOL to ground. To select the 10% level, connect TOL to
VCC. The reset outputs will remain in their active states until VCC has been continuously in-tolerance for a minimum of 250ms (the reset active time) to allow the power supply and μP to stabilize.
The RST output both sinks and sources current, while
the RST output, an open-drain MOSFET, sinks current
only and must be pulled high.

As a watchdog:

The microprocessor drives the ST input with an
input/output (I/O) line. The microprocessor must toggle
the ST input within a set period (as determined by TD)
to verify proper software execution. If a hardware or
software failure keeps ST from toggling within the minimum timeout periodâ€"ST is activated only by falling
edges (a high-to-low transition)â€"the MAX1232 reset
outputs are forced to their active states for 250ms
(Figure 2). This typically initiates the microprocessor’s power-up routine. If the interruption continues, new reset pulses are generated each timeout period until ST is strobed. The timeout period is determined by the TD input connection. This timeout period is typically 150ms with TD connected to GND, 600ms with TD floating, or 1200ms with TD connected to VCC.
The software routine that strobes ST is critical. The
code must be in a section of software that executes frequently enough so the time between toggles is less
than the watchdog timeout period. One common technique
controls the microprocessor I/O line from two
sections of the program. The software might set the I/O
line high while operating in the foreground mode, and
set it low while in the background or interrupt mode. If both modes do not execute correctly, the watchdog
timer issues reset pulses.

Tamir: Why are summarizing the datasheet? Will you take the full responsibility that your summary is 100% correct, and doesn't miss anything important?

A student will only learn by read the real datasheet, and then come back with questions if there are sections that are hard to understand.

A "professsional" shouldn't even ask this kind of questions, but switch to something they are more proficient in.

My deepest apologies...

Per: Not that it makes me feel any better now that I got reprimanded, but at least I'm sure "Jack Sprat" would be proud of me. At last, somebody in this forum reads the manual! Hipi!

Hey guys, ive been having some issues with ShowMenu for the 8052........major issues. It doesnt matter what version i use, every single time i try it on my 8052 it gives me an black screen and goes back to the main menu. Any help in this would be highly appreciated.

Lord_Duko

"At last, somebody in this forum reads the manual! Hipi!"

I downloaded the datasheet and made sure that the relevant information was easy to find before I wrote my original response :p

The problem is how to get people to understand that the majority of all datasheets are quite simple to read, and that there are no real alternatives to reading them.

Without reading the datasheet, it is impossible to really understand why something works, or why it doesn't work, or why it may look like working even if the implementation is incorrect.