SO8QG8 3.3volt interface to 5v logic (eg LCD) ?

[glennp]

Hi

I have never used 3.3v uP chips before and was wondering what is the preffered method of interfacing the 3.3v SO8QG8 parts to an LCD module for example that runs on 5v supply.?

At this stage I would like to connect my DEMO QG8 board to an LCD.  Software is not a problem, just the physical interface.

Glenn

[paul]

I have used the 9S08QG8 connected directly to 5V LCD module (write only mode). The LCD modules I use have the spec of VinH 2.2Vmin,   VinL 0.6Vmax . It works just great for me.

[bigmac]

Hello Glenn,

For a 5 volt LCD module, you might consider using a buffer from the 74HCT logic family, (and power this from the same supply as the LCD).  The inputs to these devices are TTL compatible, and should work with a 3.3 volt logic swing.  If you need to convert any 5 volt output levels down to 3.3 volts, simply use a resistive voltage divider.

Regards,

Mac

[bigmac]

Hello Glenn,

I stand corrected.

As others have pointed out, the HD44780 device (and similar clones), used within the alphanumeric LCD modules, have TTL input logic thresholds.

Regards,

Mac

[baddad]

ADI (Analog Devices) makes a cool bi-directional level translator that does not need direction control signals.

The ADG3308 can handle any voltages between 1.2V and 5.5V.

Two notes of caution:

1) note that the Y side voltage must always be equal or greater than the A side.

2) if any of the lines are shared by other pins (like a bus), care needs to be taken to avoid bus contention since all lines are always connected.

BadDad

[glennp]

Many thanks, Mac

Glenn

[Geezer]

The eval board we bought uses a 74HCT244 as the level booster. Our in-house design, which works just fine, omits it. Our LCD (a 5V part) is configured as WRITE-ONLY, and driven directly from PORTA of a GT16A. Keeps on ticking, a 3.3 swing is fine with **most** TTL. However my lawyer says I should say: the LCD manufacturer's specs always rule.