diff --git a/blk/076 b/blk/076
index 60e7f8b..a662b31 100644
--- a/blk/076
+++ b/blk/076
@@ -1,6 +1,6 @@
 STACK OVERFLOW PROTECTION: To avoid having to check for stack
 underflow after each pop operation (which can end up being
-prohibitive in terms of costs), we give ourselves a nice 6
-bytes buffer. 6 bytes because we seldom have words requiring
-more than 3 items from the stack. Then, at each "exit" call we
-check for stack underflow.
+prohibitive in terms of costs), PS_ADDR should be set to
+at least 6 bytes before its actual limit. 6 bytes because we
+seldom have words requiring more than 3 items from the stack.
+Then, at each "exit" call we check for stack underflow.
diff --git a/blk/081 b/blk/081
index c4aa45a..02086c2 100644
--- a/blk/081
+++ b/blk/081
@@ -1,5 +1,4 @@
-(cont.)
-RAMSTART  INITIAL_SP           +55       (key) override
+RAMSTART  FUTURE USES          +55       (key) override
 +02       CURRENT              +57       readln's variables
 +04       HERE                 +59       blk's variables
 +06       C<?                  +5b       z80a's variables
@@ -13,4 +12,5 @@ RAMSTART  INITIAL_SP           +55       (key) override
 +53       (emit) override
 
 
+
                                                         (cont.)
diff --git a/blk/082 b/blk/082
index 7253cf7..a3cbc48 100644
--- a/blk/082
+++ b/blk/082
@@ -1,6 +1,3 @@
-INITIAL_SP holds the initial Stack Pointer value so
-that we know where to reset it on ABORT
-
 CURRENT points to the last dict entry.
 
 HERE points to current write offset.
@@ -13,4 +10,7 @@ C<* holds routine address called on C<. If the C<* override
 at 0x08 is nonzero, this routine is called instead.
 
 
+
+
+
                                                         (cont.)
diff --git a/blk/280 b/blk/280
index 52b3fef..5e6905c 100644
--- a/blk/280
+++ b/blk/280
@@ -1,16 +1,16 @@
 Z80 boot code
 
 This assembles the boot binary. It requires the Z80 assembler
-(B200) and cross compilation setup (B260).
+(B200) and cross compilation setup (B260). It also requires
+these constants to be set:
 
-On top of that, it requires RAMSTART to be defined as the
-beginning address of RAM. This is where system variables are
-placed. HERE is then placed at RAM+80 (ref B80).
+RAMSTART: beginning address of RAM. This is where system
+variables are placed. HERE is then placed at RAM+80 (ref B80).
 
-We also need RS_ADDR to be set to the bottom address of the
-Return Stack.
+RS_ADDR: to be set to the bottom address of the Return Stack.
 
-RESERVED REGISTERS: At all times, IX points to RSP TOS and IY
-is IP. SP points to PSP TOS, but you can still use the stack\
-in native code. you just have to make sure you've restored it
-before "next".                                          (cont.)
+PS_ADDR: top address of the Parameter stack (PS grows down-
+wards). Allow space for stack underflow protection (B76).
+
+
+                                                        (cont.)
diff --git a/blk/281 b/blk/281
index 0a2d910..93a47bb 100644
--- a/blk/281
+++ b/blk/281
@@ -1,7 +1,12 @@
-(cont.) STABLE ABI: The boot binary starts with a list of
-references. The address of these references have to stay to
-those addresses. The rest of the Collapse OS code depend on it.
-In fact, up until 0x67, the (?br) wordref, pretty much
-everything has to stay put.
+RESERVED REGISTERS: At all times, IX points to RSP TOS and IY
+is IP. SP points to PSP TOS, but you can still use the stack\
+in native code. you just have to make sure you've restored it
+before "next".
+
+STABLE ABI: The boot binary starts with a list of references.
+The address of these references have to stay to those addr-
+esses. The rest of the Collapse OS code depend on it. In fact,
+up until 0x67, the (?br) wordref, pretty much everything has
+to stay put.
 
 To assemble, run "282 LOAD".
diff --git a/blk/289 b/blk/289
index dd0fc4d..465de47 100644
--- a/blk/289
+++ b/blk/289
@@ -3,8 +3,7 @@ L1 BSET 'B' A, 'O' A, 'O' A, 'T' A, 0 A,
 
 PC ORG @ 1 + ! ( main )
 ( STACK OVERFLOW PROTECTION: See B76 )
-    SP 0xfffa LDddnn,
-    RAMSTART SP LD(nn)dd, ( RAM+00 == INITIAL_SP )
+    SP PS_ADDR LDddnn,
     IX RS_ADDR LDddnn,
 ( HERE begins at RAMEND )
     HL RAMSTART 0x80 + LDddnn,
diff --git a/blk/299 b/blk/299
index 295934b..d547d8f 100644
--- a/blk/299
+++ b/blk/299
@@ -1,14 +1,10 @@
 PC ORG @ 0x1e + ! ( chkPS )
     HL PUSHqq,
-    RAMSTART LDHL(nn), ( RAM+00 == INITIAL_SP )
 ( We have the return address for this very call on the stack
-  and protected registers. Let's compensate )
-    HL DECss,
-    HL DECss,
-    HL DECss,
-    HL DECss,
+  and protected registers. 4 - is to compensate that. )
+    HL PS_ADDR 4 - LDddnn,
     SP SUBHLss,
     HL POPqq,
-    CNC RETcc,      ( INITIAL_SP >= SP? good )
+    CNC RETcc,      ( PS_ADDR >= SP? good )
     JR, L2 BWR      ( abortUnderflow-B298 )
 
diff --git a/blk/310 b/blk/310
index b1eef80..19cc92b 100644
--- a/blk/310
+++ b/blk/310
@@ -9,7 +9,7 @@ CODE PICK
     B (HL) LDrr,
     ( check PS range before returning )
     EXDEHL,
-    RAMSTART LDHL(nn), ( RAM+00 == INITIAL_SP )
+    HL PS_ADDR LDddnn,
     DE SUBHLss,
     CC L2 @ JPccnn,    ( abortUnderflow-B298 )
     BC PUSHqq,
diff --git a/blk/313 b/blk/313
index 2e72338..ed592ac 100644
--- a/blk/313
+++ b/blk/313
@@ -1,5 +1,5 @@
 CODE S0
-    RAMSTART LDHL(nn), ( RAM+00 == INITIAL_SP )
+    HL PS_ADDR LDddnn,
     HL PUSHqq,
 ;CODE
 
diff --git a/blk/327 b/blk/327
index 94c2e81..038c5cd 100644
--- a/blk/327
+++ b/blk/327
@@ -3,8 +3,7 @@ CODE BYE
 ;CODE
 
 CODE (resSP)
-    ( INITIAL_SP == RAM+0 )
-    SP RAMSTART LDdd(nn),
+    SP PS_ADDR LDddnn,
 ;CODE
 
 CODE (resRS)
diff --git a/emul/forth.bin b/emul/forth.bin
index f9614a4..99c6482 100644
Binary files a/emul/forth.bin and b/emul/forth.bin differ
diff --git a/emul/xcomp.fs b/emul/xcomp.fs
index e7b63f4..07c4963 100644
--- a/emul/xcomp.fs
+++ b/emul/xcomp.fs
@@ -1,5 +1,6 @@
 0xe800 CONSTANT RAMSTART
 0xf000 CONSTANT RS_ADDR
+0xfffa CONSTANT PS_ADDR
 212 LOAD  ( z80 assembler )
 262 LOAD  ( xcomp )
 : CODE XCODE ;
diff --git a/recipes/rc2014/xcomp.fs b/recipes/rc2014/xcomp.fs
index 6f08080..903cade 100644
--- a/recipes/rc2014/xcomp.fs
+++ b/recipes/rc2014/xcomp.fs
@@ -1,5 +1,6 @@
 0x8000 CONSTANT RAMSTART
 0xf000 CONSTANT RS_ADDR
+0xfffa CONSTANT PS_ADDR
 0x80   CONSTANT ACIA_CTL
 0x81   CONSTANT ACIA_IO
 4      CONSTANT SDC_SPI
diff --git a/recipes/ti84/xcomp.fs b/recipes/ti84/xcomp.fs
index 0b0dd8c..5d142e3 100644
--- a/recipes/ti84/xcomp.fs
+++ b/recipes/ti84/xcomp.fs
@@ -1,5 +1,6 @@
 0x8000 CONSTANT RAMSTART
 0xb000 CONSTANT RS_ADDR
+0xbffa CONSTANT PS_ADDR
 RAMSTART 0x70 + CONSTANT LCD_MEM
 RAMSTART 0x72 + CONSTANT KBD_MEM
 0x01 CONSTANT KBD_PORT
diff --git a/recipes/trs80/xcomp.fs b/recipes/trs80/xcomp.fs
index 2db7e2b..0f3ebb5 100644
--- a/recipes/trs80/xcomp.fs
+++ b/recipes/trs80/xcomp.fs
@@ -1,4 +1,5 @@
 0xf000 CONSTANT RS_ADDR
+0xfffa CONSTANT PS_ADDR
 RS_ADDR 0x80 - CONSTANT RAMSTART
 212 LOAD  ( z80 assembler )
 262 LOAD  ( xcomp )