Super IO chip lpt port challenge

Hello fellow boardmembers

This is my first post on the board, which I have lurked at for some time, but only joined just now. So be gentle :lol:

I am tasked with designing a ruggedized computer based on a q-seven module. The kicker for this computer is that it, among other things, needs 6 serial ports and an lpt port.
Due to the part being available within our organisation, I have to use the SMSC SCH3116 part, which has exactly that.

Our main customer wants to interface some legacy 5V equipment to the lpt port, but the SMSC part is 3v3 only. So my question is: has anyone here tried converting an lpt port from 3v3 to 5v without loosing any of its flexibility? Any pointers, hints, schematics excerpts are gladly appreciated.

Thanking you all in advance.

Br
Henrik

The data sheet I found of the SMSC SCH3116 does not specilify clearly what the input signal value must be. If there are 3.3V LPC-inputs on the SCH3116, then it could be usefull to protect the inputs to the maximum allowed voltage( e.g. resitor in serie with a diode to 3.3V). If the output signal of the LPC-port are only 3.3V logic level it works most time with normal TTL-input. If not you could connect level shifter to (like descibed here: https://ichaus.biz/wp1_mcu_interface ).

Enjoy your design work!

Hello HTA

Thanks for you reply. I was considering the levelshift myself, by using buffers etc but fell short on the bidirectional part of it. Sadly I am required to retain the full EPP/ECP capabilities of the lpt port, while still adhering to the 5V interface specification. I did no immediately see a way to solve this.

Other than that, I enjoy the design work alot, finished the power supply tree today. It is actually going to a sweet little device

Br
Henrik

Hello Henrik,

great! There was another thread on this topic with links to interfacing manual. Please see: https://www.edaboard.com/threads/273541/ and maybe you find somethink useful.

Br Horst