Safely connecting 4056 and MSP430

[Ari123 L. (Firma: Kynix Semiconductor HongKong L) (yumi1)]

I'm using MSP430G2553IN20 
microcontroller(http://www.kynix.com/Detail/569447/MSP430G2553IN20.html) 
on LaunchPad to drive an 4056 chip (HCF4056B to be precise) and a 7 
segment display. The 4056 is set to sink current.

I've connected the port 2 pins, set as outputs, to the BCD and STROBE 
input pins of the 4056. The board with 4056 and display has its own 
separate power supply and the MSP430 is powered via the LaunchPad which 
provides it around 3.6 V. The grounds of both supplies are connected and 
I've set the other power supply as close as possible to 3.6 V.

I'm concerned that with this setup I could damage the chips. For 
example, when the 4056 power is down, it and the display are still 
getting some power from the MSP430 via the BCD and STROBE pins and the 
display remains on, although sometimes it works incorrectly.

Right now, I'm using 220 Ω220 Ω resistors on the output pins of the 
MSP430 to limit the output current, but I'm afraid that the setup isn't 
safe enough.

So my question is: Is there a simple and safe way to connect the MSP430 
to the 4056? For best results, I'd want to drive 4056 at higher voltage 
than MSP430, but if that's too difficult I could settle for 3.6 V.

[Clemens L. (c_l)]

A level shifter like the SN74LVC8T245 could drive up to 5 V, and would 
isolate both sides if one supply is at 0 V.

For higher voltages, check out CD4504B or CD40109B.

[Jim M. (turboj)]

Ari123 L. schrieb:
> Right now, I'm using 220 Ω220 Ω resistors on the output pins of the
> MSP430 to limit the output current, but I'm afraid that the setup isn't
> safe enough.

Those two GPIO pins can drive the resulting ~16mA current each all day 
long.

Why should this setup not be safe "enough"? Please elaborate.