Quick function transformation...

Hey guys,
I've been struggling with this for a while and was wondering if you guys could help me turn this function from javascript to php:

// CONVERTS *ALL* CHARACTERS INTO ESCAPED VERSIONS.
function escapeTxt(os){
	var ns='';
	var t;
	var chr='';
	var cc='';
	var tn='';
	for(i=0;i<256;i++){
		tn=i.toString(16);
		if(tn.length<2)tn="0"+tn;
		cc+=tn;
		chr+=unescape('%'+tn);
	}
	cc=cc.toUpperCase();
	os.replace(String.fromCharCode(13)+'',"%13");
	for(q=0;q<os.length;q++){
		t=os.substr(q,1);
		for(i=0;i<chr.length;i++){
			if(t==chr.substr(i,1)){
				t=t.replace(chr.substr(i,1),"%"+cc.substr(i*2,2));
				i=chr.length;
			}
		}
	ns+=t;
	}
	return ns;
}

Code (markup):

All help will be deeply appreciated.
Thank you.