Using P0 port for driving +3.3 V Devices

I have a question. Don't you think it would be relevant to specify exactly what 8051 chip you have, since there are thousands and thousands of different manufacturers and models available?

In the general case, the answer is no. But the datasheet for your specific chip can tell you what voltage levels the pin inputs requires to be safely detected as high or low. And the datasheet for your 3.3V device will tell what voltages it emits as high or low.

In the other direction, where the 8051 pin is output, it depends a lot on if your specific chip have a pseudo output with a pull-up to 3.3V or if it forcibly drives the signal to +5V. And it depends a lot on if the external hardware is 5V tolerant - some 3.3V chips have 5V-tolerant inputs, i.e. output signals swings between 0 an 3.3V while inputs are detected as low or high in the 3.3V range but allowed to be drawn to 5V without problems.

Without more information from you, we can't really help you but tell you to read the datasheets. You might have to add resistors or level converters between the two chips. But your didn't even spent the time to tell your signal directions.

Hello,

Thanks for the prompt reply.

Sorry for the incomplete information. The details are as follows.

The Controller is Atmel make AT89S52, 8 bit micro controller with 4K bytes of in system programmable flash. This controller is compabile with industry standard 8051 for general functions and IO pins.

The control functionality we are proposing is two way for the same port i.e it will be used as write as well as read pin for sending the command and acquiring the data from same port.

With regards

for most (and I believe the AT89S52 - check the datasheet) old fashioned '51 derivatives P0 is 'open drain' which means that there is no pullup on the pins. Thus if you pull up with resistors connected to 3V3 this will, for output be a 3V3 bus. For input to PO you will have to check the output range (Voh Vol) of your other chip vs the input range of (Vih Vil) the AT chip and beware that you maintain a decent noise margin.

Erik

Thanks for the information.

With regards