topic MC9S08GT16A buffering inputs in 8-bit Microcontrollers

MC9S08GT16A buffering inputs

Kerms — Sun, 02 Dec 2007 09:54:32 GMT

Hello, I am using an MC9S08GT16A to interface with several 5v sensors. As such I need to buffer the inputs to make them 5v input tolorent.

I am looking to use the 74LCX240 to buffer the inputs and was wondering if that was a good choice or if there are others I should use instead.

Also can you recommend any bi directional buffers if I wanted to be able to change the direction?

Thanks

Re: MC9S08GT16A buffering inputs

peg — Sun, 02 Dec 2007 10:47:04 GMT

Hi Kerms,

That part would seem to be OK.
Have you looked at AN2433
SN74LVC1T45DBV is an example of a bi-directional buffer.

Re: MC9S08GT16A buffering inputs

Witztronics — Sun, 02 Dec 2007 11:44:27 GMT

Check out the ADI ADG330x family of parts.

http://www.analog.com/en/prod/0,,767_828_ADG3304%2C00.html

They don't need directional pins.

Message Edited by Witztronics on 2007-12-01 10:45 PM

Re: MC9S08GT16A buffering inputs

bigmac — Sun, 02 Dec 2007 15:10:33 GMT

Hello,

If the sensors you refer to are the channel outputs from a RC receiver (as described in another post), a satisfactory interface method may be to simply provide a series resistor (say 4k7) for each input. The intrinsic protection diodes will limit the voltage swing. Alternatively, you could add an external Schottky diode between each input (anode) and +3V3 (cathode). The external diode should conduct before the intrinsic diode does. In both cases, the series resistor will limit current flow.

A related method would be to provide a voltage divider to provide 3V3 output for an input of 5V.

For any outputs from the MCU, you should first examine whether the external device will operate correctly with a 3V3 swing.

Regards,

Mac

Re: MC9S08GT16A buffering inputs

Technoman64 — Sun, 02 Dec 2007 16:10:35 GMT

I have used the following Tiny Logic part to succesfully interface +5v to +3.3v logic. The inputs are 5 volt toleant when operating with a 3.3 volt supply.

SN74LVC1G17