Port 1 on 3400 family not 5 Volt compatible?

[dschulmi]

Posted on January 03, 2008 at 09:13

Port 1 on 3400 family not 5 Volt compatible?

[dschulmi]

Posted on May 17, 2011 at 12:09

I have read on the upsd34xx datasheet that MCU Port 1 is not 5 Volt IO Tolerant. What does it mean? Could I not drive/be driven by a peripheral 5 Volt TTL compatible? What range of voltage does it manage?

Thanks

[hanwayh]

Posted on May 17, 2011 at 12:09

Hello:

What this means is that the high output of the uPDS pin may not be high enough for the 5-V I/O device (so won't be interpreted as logic 1) and the low output voltage from an I/O device with 5-V power supply may be too high to be considered as low (logic 0) for the uPDS input pin.

Han-Way

[sunsy]

Posted on May 17, 2011 at 12:09

in fact, P1.x is 1.6V only when I set it as GPIO and output '1'.

in case as drive led, works with 9013 and a 510R R, P1.0 was pulled down to 0.6V.

Mygod, what should i do?

[redmonds]

Posted on May 17, 2011 at 12:09

Do you mean ''Port 1 on 3400 family not 5 Volt tolerant?''

Other ports on 34xx have protection to allow connection of 5V sources to without causing damage if the MCU is powered from 3V3. Port 1 does not have this protection (due to its alternative use as an adc input) and so damage may occur. Take care - I damaged a Port 1 pin simply by reworking a part connected to it.

[redmonds]

Posted on May 17, 2011 at 12:09

When using port pins for high current, remember that Ports 1, 3, 4 are quasi-bidirectional. This means that when a '1' is written to the corresponding SFR bit, the output will go high, but will have a source impedance of 150K. This is fine for connecting to other digital logic, but insufficient for driving LEDs.

When a '0' is written to the corresponding SFR bit, the output will go low and will be sufficiently low impedance to sink mA (depending on port and supply voltage). So if you want to drive LEDs, invert the logic so that the LED is connected to rail and the port pin pulls low.