diff --git a/blk/690 b/blk/690
index 0a3ade7..27feaaa 100644
--- a/blk/690
+++ b/blk/690
@@ -4,4 +4,4 @@ This program allows you to access AVR chips Flash memory, EEPROM
 and fuses using a SPI relay. This requires drivers that imple-
 ment the SPI Relay protocol.
 
-Load range: B691-BXXX
+Load range: B691-B693
diff --git a/blk/691 b/blk/691
index cb76f2f..2b618ba 100644
--- a/blk/691
+++ b/blk/691
@@ -1,14 +1,15 @@
-: _cmd ( b4 b3 b2 b1 -- r4 )
-    (spix) DROP DUP (spix) DROP SWAP (spix) = ( b4 f )
-    SWAP (spix) SWAP ( r4 f ) NOT IF ABORT" AVR err" THEN ;
+( page size in words, 64 is default on atmega328P )
+CREATE aspfpgsz 64 ,
+VARIABLE aspprevx
+: _x ( a -- b ) DUP aspprevx ! (spix) ;
+: _xc ( a -- b ) DUP (spix) ( a b )
+    DUP aspprevx @ = NOT IF ABORT" AVR err" THEN ( a b )
+    SWAP aspprevx ! ( b ) ;
+: _cmd ( b4 b3 b2 b1 -- r4 ) _xc DROP _x DROP _xc DROP _x ;
+: asprdy ( -- ) BEGIN 0 0 0 0xf0 _cmd 1 AND NOT UNTIL ;
 : asp$ ( -- )
     ( RESET pulse ) (spie) (spid) (spie)
-    ( wait 20ms ) 2000 0 DO LOOP
-    ( enable prog ) 0 0 0x53 0xac _cmd DROP ;
-: asprdy ( -- f ) 0 0 0 0xf0 _cmd NOT ;
-: aspfl@ ( -- lfuse ) 0 0 0 0x50 _cmd ;
-: aspfh@ ( -- hfuse ) 0 0 0x08 0x58 _cmd ;
-: aspfe@ ( -- efuse ) 0 0 0x00 0x58 _cmd ;
-: aspfl! ( lfuse -- ) 0 0xa0 0xac _cmd ;
-: aspfh! ( hfuse -- ) 0 0xa8 0xac _cmd ;
-: aspfe! ( efuse -- ) 0 0xa4 0xac _cmd ;
+    ( wait >20ms ) 5000 0 DO LOOP
+    ( enable prog ) 0xac (spix) DROP
+    0x53 _x DROP 0 _xc DROP 0 _x DROP ;
+: asperase 0 0 0x80 0xac _cmd asprdy ;
diff --git a/blk/692 b/blk/692
new file mode 100644
index 0000000..37f2327
--- /dev/null
+++ b/blk/692
@@ -0,0 +1,7 @@
+( fuse access. read/write one byte at a time )
+: aspfl@ ( -- lfuse ) 0 0 0 0x50 _cmd ;
+: aspfh@ ( -- hfuse ) 0 0 0x08 0x58 _cmd ;
+: aspfe@ ( -- efuse ) 0 0 0x00 0x58 _cmd ;
+: aspfl! ( lfuse -- ) 0 0xa0 0xac _cmd ;
+: aspfh! ( hfuse -- ) 0 0xa8 0xac _cmd ;
+: aspfe! ( efuse -- ) 0 0xa4 0xac _cmd ;
diff --git a/blk/693 b/blk/693
new file mode 100644
index 0000000..3c931c4
--- /dev/null
+++ b/blk/693
@@ -0,0 +1,13 @@
+: aspfb! ( n a --, write word n to flash buffer addr a )
+    SWAP 256 /MOD ( a lo hi ) SWAP ROT ( hi lo a )
+    DUP ROT ( hi a a lo ) SWAP ( hi a lo a )
+    0 0x40 ( hi a lo a 0 0x40 ) _cmd DROP ( hi a )
+    0 0x48 _cmd DROP ;
+: aspfp! ( page --, write buffer to page )
+    0 SWAP aspfpgsz @ * 256 /MOD ( 0 lsb msb )
+    0x4c _cmd DROP asprdy ;
+: aspf@ ( page a -- n, read word from flash )
+    SWAP aspfpgsz @ * OR ( addr ) 256 /MOD ( lsb msb )
+    2DUP 0 ROT ROT ( lsb msb 0 lsb msb )
+    0x20 _cmd ( lsb msb low )
+    ROT ROT 0 ROT ROT ( low 0 lsb msb ) 0x28 _cmd 8 LSHIFT OR ;
diff --git a/doc/avr.txt b/doc/avr.txt
index a40318c..70b3a47 100644
--- a/doc/avr.txt
+++ b/doc/avr.txt
@@ -48,3 +48,22 @@ batch, that is, running your commands right after the "asp$" command, ending
 your batch with "(spid)" so that the next batch works. In my tests, interacting
 with the chip "live" in a single "asp$" session sometimes resulted in unreliable
 data that didn't properly detect sync errors. TODO: investigate further.
+
+# Writing data to Flash
+
+Writing to AVR's flash is done in batch mode, page by page. To this end, the
+chip has a buffer which is writable byte-by-byte. To write to the flash, you
+begin by writing to that buffer using aspfb! and then write to a page using
+aspfp!.
+
+Please note that aspfb! deals with *words*, not bytes. If, for example, you want
+to hook it to A!*, make sure you use AMOVEW instead of AMOVE. You will need to
+create a wrapper word around aspfb! that divides dst addr by 2 because AMOVEW
+use byte-based addresses but aspfb! uses word-based ones. You also have to make
+sure that A@* points to @ (or another word-based fetcher) instead of its default
+value of C@.
+
+Beware of bootloader sections! By default, AVR chips have a bootloader using the
+first few pages (by default, the ATMega328P uses 4 pages for its bootloader).
+Check (or modify) the BOOTSZ fuses to confirm where you whould start writing
+your program.