Connecting a T6963c based LCD

[Marc VDH]

I was wondering if a Toshiba T6963C based graphical LCD module can be connected directly to a Coldfire microcontroller, as the Toshiba chips are specified to work at a power supply voltage of 5V only. Or do they also work at 3,3V?

[mark]

Hi Marc

Using a level shifter it is certainly possible.

Without level shifters it shouldn't be a problem to write to the display - the 3V3 (approx.) driven from the processor should be safely recognised correctly as '0' / '1'. When reading from the display it will drive up to 5V to the processor. Since the Coldfires are not "truely" 5V tolerant it is advisable to insert current limiting resistors in series. See this recommendation from a Freescale forum moderator: http://forums.freescale.com/freescale/board/message?board.id=CFCOMM&message.id=1115&query.id=152245#M1115

Generally I do still wonder about the fact that most LCDs are still 5V types since it is always a bit uncomfortable interfacing them to 3V3 processors. Some LCDs can be used at both 5V and 3V3 whereby the difference is that their timing is a little slower at 3V3 and this often causes complications with the contrast voltage usually applied to them (unless they have internal control). Typically a 5V LCD (I have more experience with graphical ones so this may not always be the case) requires a small positive voltage on its contrast input, whereby the actual current is sourced by the display and so a resistor to ground of the correct value may be adequate. 3V3 types tend to require a slightly negative voltage, which can lead to the additional requirement for a negative voltage generator (eg. a charge pump circuit) to be added. To avoid the latter a 5V display still turns out to be the simplest to use...

Regards

Mark