A320 WITH ZDV AT FL360 RECEIVED TCAS RA AFTER SOME UNCERTAINTY REGARDING ALT ASSIGNMENT; PLTDEV RECORDED.

Narrative

WE WERE LEVEL AT FL360 WHEN THE FO WENT BACK TO USE THE RESTROOM. WHILE THE FO WAS GONE; ZDV ISSUED A DSCNT CLRNC TO FL340; WHICH I READ BACK AND SET FL340 IN THE WINDOW (I AM CERTAIN I DID THIS). JUST BEFORE THE FO ENTERED THE FLT DECK; I PULLED FOR AN OPEN DSCNT. WHEN THE FO ENTERED; I WAS REVIEWING THE GRANDPA 1 ARR. JUST AS THE FO WAS GETTING INTO HIS SEAT; I SAID TO HIM; 'THE ONLY CHANGE IS A DSCNT TO FL340.' NO SOONER DID I SAY THAT; WHEN ZDV ASKED (AND I AM NOT EXACTLY SURE HOW THEY PHRASED IT). 'WHAT IS YOUR ASSIGNED ALT?' I DON'T REMEMBER IF I SAID FL340 OR LOOKED AT WHAT WAS SET IN THE ALT WINDOW AND READ THAT BACK. IN THIS CASE IT MAY HAVE BEEN FL330. THE NEXT INSTRUCTIONS FROM DENVER WERE TO CLB; WHICH I COMPLIED WITH IMMEDIATELY BY DISCONNECTING THE AUTOPLT. AS SOON AS I STARTED THE CLB; WE RECEIVED A TCAS RA DSCNT COMMAND. WE HAD TFC IN SIGHT; AND THEY WERE BELOW US. WITHIN 2 SECONDS OF GETTING THE DSND RA; WE GOT A CLB RA WHICH WE COMPLIED WITH; CLRED THE CONFLICT; AND REACHED OUR ALT VERY QUICKLY. MOMENTS LATER; ZDV ASKED US TO GIVE THEM A CALL. REMAINDER OF FLT WAS NORMAL. ONCE ON THE GND AND PARKED AT THE GATE; I GAVE ZDV A CALL. AFTERWARDS; THE FO AND I DISCUSSED WHAT HAPPENED AND WE AGREED THAT IF THERE WERE 2 PLTS ON THE FLT DECK; THIS INCIDENT WOULD NOT HAVE HAPPENED. WHAT I BELIEVED HAPPENED; IS THAT WHEN I PULLED FOR OPEN DSCNT; I POSSIBLY CHANGED THE FLT ALT FROM FL340 TO FL330. I WOULD ALSO LIKE TO MENTION THAT THE DIGITS IN THE DISPLAY WERE EXTREMELY POOR. AT ONE POINT; I HAD TO PUT MY HAND ABOVE THE NUMBERS SO WE WERE ABLE TO READ THEM.