LE : Solution (not so elegant, but working) :
Code:
Main:
;reading buttons on row 1
PortA.0 = 0
TrisA.1 = 1
pause 10
if porta.2 = 0 then
  portb.1 = 1
while porta.2=0 :  wend
  portb.1 = 0 
endif

if porta.3 = 0 then
  portb.2 = 1
while porta.3=0 :  wend
  portb.2 = 0
endif
                
if porta.4 = 0 then
  portb.3 = 1
while porta.4=0 : wend
  portb.3 = 0
endif

PortA.0 = 1
TrisA.1 = 0


;reading buttons on line 2    
Portb.0 = 0
TrisA.1 = 1
pause 10
if porta.2 = 0 then
  portb.4 = 1
while porta.2=0 :  wend
  portb.4 = 0 
endif

if porta.3 = 0 then
  portb.5 = 1
while porta.3=0 :  wend
  portb.5 = 0
endif
                
if porta.4 = 0 then
  portb.6 = 1
while porta.4=0 : wend
  portb.6 = 0
endif

Portb.0 = 1
TrisA.1 = 0
    
Goto main