let kbbuff = vec(25),
    kbbs = 0, kbbe = 0, kbbn = 0, kbbmax = 99, kbblines = 0;

...

let kbbadd(c) be
{ if kbbn >= kbbmax then resultis 0;
  byte kbbe of kbbuff := c;
  if c = '\n' then kbblines +:= 1;
  kbbn +:= 1;
  kbbe +:= 1;
  if kbbe > kbbmax then kbbe := 0;
  resultis 1 }

...

let kbbremove() be
{ let c;
  if kbblines = 0 then resultis 0;
  c := byte kbbs of kbbuff;
  kbbn -:= 1;
  kbbs +:= 1;
  if kbbs > kbbmax then kbbs := 0;
  if c = '\n' then kbblines -:= 1;
  resultis c }

let getchar() be
{ ...
  c := kbbremove();
  ... }

let keyboard_handler() be
{ ...
  kbbadd(c)
  ... }