Interfacing 7 segment display with msp430 launchpad

Let's ask google first. Click the link below.

     http://lmgtfy.com/?q=msp430+4511+segment+driver

-kel

Agree w/ Kel's Google suggestion.  You must become more resourceful to better succeed both in school & thereafter.

Your 4511 requires 4 data bits to produce 0-9 numeric representations upon display.  And - you have a "strobe" pin on the 4511 - which critically enables those 4 data bits to see additional use. 

To conserve MCU GPIO - you may connect those same 4 MCU GPIO/data pins in parallel - to each 4511.  Trick then is to harvest 2 more GPIO - connect one each to the strobe pin of 4511.  (unique strobe connections)  In so doing you've reduced the GPIO requirements from 8 to 6.  Only that data present @ the moment the targeted 4511 receives the strobe signal will be latched into that particular 4511 - 2nd 4511 will be unaffected.  Repeat this process for the 2nd 4511 -> digit.

And - you can save even more GPIO.  Multiplexing enables a single 4511 to drive multiple 7 Segment Leds.  Technically this technique is called, "Time Division Multiplexing" and is achieved by strobing data into that single 4511 @ 100Hz or so rates - and employing an extra GPIO (w/ some current buffering i.e. transistor) to pull the common cathode of each display to ground - in that particular display's "ON" period.  This is followed by brief "All OFF" period - and then method is repeated for next display.  We've employed this single 4511 to drive up to 6 efficient, common cathode, LED displays.  In your "unusual" 2 digit display case - six GPIO are required which "breaks even" with the dual 4511 - strobe-technique - described para. above. 

Certain MCUs have GPIO w/the current capability to directly interface to a 7 segment Led.  Multiplex method is usually employed - and additional GPIO provide the necessary switch drive to external transistors which enable each display to be sequentially driven/scanned.  Done quickly enough (i.e. 100Hz usually works) the observer cannot tell that the digits are not, "always on."   (but you can achieve this recognition - by moving your head rapidly - you'll then slightly note the scan...)

Green Verify Answer tick much appreciated - s'il vous plait.

archita mamani said:

which pins are to be connected to MCU

You have great flexibility in MCU -> 4511 pin selection. 

To ease SW - suggest that you choose 2 separate MCU ports - one for data - 2nd for strobe control.  This separation of MCU ports eases your job as it is less likely that the 2 port method will enable output from the data port to "disturb" the strobe port - and vice-versa.

Suggest that you choose MCU Port bits D0-D3 for data - in this manner the data you output has direct correlation with what will be displayed.  (i.e. data_port = 3; will produce a "3" on the display; data_port = 8; will yield an "8.")  You wire MCU D0 to D0 of both 4511s.  (and Dn to Dn - similarly)

It has been good 20+ years since our group used 4511 - but I believe the strobe/latch input is "edge" (not level) sensitive.  If you connect D0 from MCU strobe_port to 4511 #1's strobe input - then strobe_port = 0; (some delay) followed by strobe_port = 1; generates a "rising edge" (check 4511 data to learn what's actually needed - I'm providing a general format solution.)  "Delay" listed may/may not be required.  4511 should list minimum "hold" time for that strobe - if it is "pulse" rather than "edge" driven.  Back to back MCU instructions may violate the pulse width requirement - delay cures. 

Test this code with only a single 4511/display connected - want to build your understanding/confidence first.  Once that's working - we must modify so that a 2nd digit can be accommodated.

Now - onto that 2nd digit - assume D1 from MCU strobe_port routes to strobe pin - 2nd 4511.  Thus strobe_port = 0, (delay) strobe_port = 2; will cause a rising edge upon 2nd 4511.  You will note that "1" and "2" are mutually exclusive - thus will not "spoil" data upon the other 4511.  But - if you wish to write the identical data to both 4511s - in just "one go" you may "strobe_port = 3;"  (delay), strobe_port = 0; .

Final consideration - suggest you attempt only after the above description has been test/verified.  Might you be able to achieve "all of the above" from 6 pins - upon a single port?  And - use some/many of that port's "other pins" - for different requirements?  Answer is Yes - if cautious.  "Magic" here is limiting your LED transactions to just the Led Data & Strobe pins.  And - limiting "other transactions" to just those selected "other pins"  - even though all of these pins are now upon the same port.  And - there's one more complication when using single port for both data & strobe.  It is tempting to output data & strobe in single instruction - and this will fail as the "hold" time required for data to stabilize - prior to the arrival of strobe - will likely be violated.  That said - if we assume "rising edge" works w/4511 - the data and strobe = 0 may be sent as one.  (i.e. together)  Then follows (delay) and then the strobe is driven high - being sure to change not other port pin content!  (critical - see below)  This explains why I've asked that you not "start" w/this more complex method - you really have to get the simpler version (para above) to work first - otherwise "krazy-making" too much in play...

If you don't "limit/confine" port transactions - you will likely "spoil" data presently output from that port - but not part of your current transaction.  Think about this - and see if you can devise a method to "confine" your transaction to just a limited number of pins - anywhere on that port...