Webで検索してみましたが見つかりませんでした。
お教えいただければ幸いです。

xx.ap.plala.or.jp - - [21/Jul/2004:11:04:00 +0900] "\xa0 \"\x1e" 400 - "-" "-"
xx.ap.plala.or.jp - - [21/Jul/2004:11:07:39 +0900] "(\x97\x9f " 501 - "-" "-"
xx.ap.plala.or.jp - - [21/Jul/2004:11:10:11 +0900] "\xb0\x01\xea\x1d" 501 - "-" "-"
xx.ap.plala.or.jp - - [21/Jul/2004:11:29:46 +0900] "PBD\x1e" 501 - "-" "-"
xx.ap.plala.or.jp - - [21/Jul/2004:11:51:25 +0900] "\xa85a\x1e" 501 - "-" "-"
xx.ap.plala.or.jp - - [21/Jul/2004:12:02:31 +0900] "x\xed\xb6 " 501 - "-" "-"
xx.ap.plala.or.jp - - [21/Jul/2004:12:08:37 +0900] "\x90\xecw\x1e" 501 - "-" "-"
xx.ap.plala.or.jp - - [21/Jul/2004:12:09:47 +0900] "x\x92y\x1e" 501 - "-" "-"
xx.ap.plala.or.jp - - [21/Jul/2004:12:14:14 +0900] "\x90e\x7f\x1e" 501 - "-" "-"
xx.ap.plala.or.jp - - [21/Jul/2004:12:14:38 +0900] "\x80\x04\x85\x1e" 501 - "-" 

-- 
Ichikawa Jun'ichi