DS89C420 maximum current it can sink and can deliver....

Hi,

I've been working 8051, DS89C420 to be specific, but just now I just realized that I am not noticing or not caring about the maximum current it can sink or deliver to a load.

Now my question, what is it's maximum current that can sink to a load, I am talking here of a single port pin.

How is that compared to a PIC.

Thanks.

Glenjoy

According to Philips book standard 8051 can sink max 15mA per pin, maximum 26mA per 8-bit port and 71mA for all outputs.
As they have only weak pull-up inside the source current will be in hundreds of µA range.

With PICs:for example 16F872
Maximum output current sunk by any I/O pin 25 mA
Maximum output current sourced by any I/O pin 25 mA
Maximum current sunk by PORTA and PORTB 200 mA
Maximum current sourced by PORTA and PORTB 200 mA
Maximum current sunk by PORTC 200 mA
Maximum current sourced by PORTC 200 mA
But these CPUs with weak pull-up will have similar range as 8051.

So that is why the 8051's cannot directly drive an output without using a buffer before them or using a pull-up.

please read data sheet DS89C420 at www.maxim-ic.com

ElecThai said:

please read data sheet DS89C420 at www.maxim-ic.com

Click to expand...

Can you tell me where in the datasheet?

For Port 0 and 2 in Bus Mode when addressing external memory, you can count on 8mA source at a minimum of 2,4v output.
If you want to deliver outside more than 8 mA you can be sure that the output voltage will significant decrease.
Which is not your goal if you want to keep compatibility with a TTL input which needs minimum 2.0v in order to be recognized as input HIGH signal.
But I'm confident you know already all these things.
For Port 1,2 and 3 you can count on 50microA delivered outside at 2,4v output voltage.
In data sheet it's mentioned and the current delivered during transition from 0 to 1 logic of these ports, which is 1,5mA, but only during transition.
You can read more about the hard drive circuit (which improve the edge slope at pin output) in the hardware 8051 bible.

For sinking currents you can count on 1,6mA on port 1 an 3 and 3,2mA for Port 0 and 2, both values providing minimum 2,4v output voltage.
Obvious you can sink more (up to the maximum rated power), but the output value will raise referenced to ground.

When your external peripheral circuit drives the input Port pin, it must be able to sink 55 microA at 0,4v and minimum 650 microA at 2v during transition from 1 to 0 logic when the Port pin is pulled down externally by peripheral circuit.

If the explanations above are boring and confusing, you can read the data sheet pag 44, table 16. DC ELECTRICAL CHARACTERISTICS

Regards
Silvio