diff --git a/Doc/RomWBW Applications.pdf b/Doc/RomWBW Applications.pdf
index 4f21039c..275b6797 100644
Binary files a/Doc/RomWBW Applications.pdf and b/Doc/RomWBW Applications.pdf differ
diff --git a/Doc/RomWBW Architecture.pdf b/Doc/RomWBW Architecture.pdf
index 2fee8c60..468e8fde 100644
Binary files a/Doc/RomWBW Architecture.pdf and b/Doc/RomWBW Architecture.pdf differ
diff --git a/Doc/RomWBW Disk Catalog.pdf b/Doc/RomWBW Disk Catalog.pdf
index 39843e0c..f5f33b31 100644
Binary files a/Doc/RomWBW Disk Catalog.pdf and b/Doc/RomWBW Disk Catalog.pdf differ
diff --git a/Doc/RomWBW Getting Started.pdf b/Doc/RomWBW Getting Started.pdf
index 0ebfa20f..225e2dda 100644
Binary files a/Doc/RomWBW Getting Started.pdf and b/Doc/RomWBW Getting Started.pdf differ
diff --git a/Source/Doc/Architecture.md b/Source/Doc/Architecture.md
index 8db85458..6260d673 100644
--- a/Source/Doc/Architecture.md
+++ b/Source/Doc/Architecture.md
@@ -410,6 +410,28 @@ require double-buffering if the caller’s buffer is in the lower 32K of CPU
 address space. For optimal performance, such buffers should be placed in
 the upper 32K of CPU address space.
 
+Error Codes
+-----------
+
+The following error codes are defined generically for all HBIOS functions.
+Most function calls will return a result in register A.
+
+_Code_ | _Meaning_
+------ | ---------
+0      | function succeeded
+-1     | undefined error
+-2     | function not implemented
+-3     | invalid function
+-4     | invalid unit numberr
+-5     | out of memory
+-6     | parameter out of range
+-7     | media not present
+-8     | hardware not present
+-9     | I/O error
+-10    | write request to read-only media	
+-11    | device timeout
+-12    | invalid configuration
+
 `\clearpage`{=latex}
 
 Character Input/Output (CIO)
diff --git a/Source/HBIOS/acia.asm b/Source/HBIOS/acia.asm
index 4f7f0ee8..4c3c1255 100644
--- a/Source/HBIOS/acia.asm
+++ b/Source/HBIOS/acia.asm
@@ -165,7 +165,7 @@ ACIA_INIT1:
 ;
 ACIA0_INT:
 ACIA1_INT:
-	CALL	PANIC
+	CALL	PANIC			; NO RETURN
 ;
 #ENDIF
 ;
diff --git a/Source/HBIOS/bqrtc.asm b/Source/HBIOS/bqrtc.asm
index f1c6a751..274a56f0 100644
--- a/Source/HBIOS/bqrtc.asm
+++ b/Source/HBIOS/bqrtc.asm
@@ -161,7 +161,10 @@ BQRTC_DISPATCH:
 	JP	Z, BQRTC_SETALM			; Set Alarm
 	DEC	A
 	JP	Z, BQRTC_DEVICE			; Report RTC device info
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOFUNC
+	OR	A
+	RET
 	
 ;
 ; NVRAM FUNCTIONS ARE NOT AVAILABLE
@@ -170,7 +173,10 @@ BQRTC_GETBYT:
 BQRTC_SETBYT:
 BQRTC_GETBLK:
 BQRTC_SETBLK:
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 	
 ; RTC Get Time
 ;   A: Result (OUT), 0=OK, Z=OK, NZ=Error
diff --git a/Source/HBIOS/cvdu.asm b/Source/HBIOS/cvdu.asm
index 1ceb847d..0cc31919 100644
--- a/Source/HBIOS/cvdu.asm
+++ b/Source/HBIOS/cvdu.asm
@@ -136,7 +136,10 @@ CVDU_VDADEV:
 	RET
 
 CVDU_VDASCS:
-	CALL	PANIC		; NOT IMPLEMENTED (YET)
+	CALL	SYSCHK		; NOT IMPLEMENTED (YET)
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 
 CVDU_VDASCP:
 	CALL	CVDU_XY		; SET CURSOR POSITION
diff --git a/Source/HBIOS/dbgmon.asm b/Source/HBIOS/dbgmon.asm
index f0c57b42..24a9f26a 100644
--- a/Source/HBIOS/dbgmon.asm
+++ b/Source/HBIOS/dbgmon.asm
@@ -1400,7 +1400,7 @@ DISPLAYBUF:	.FILL	8,0
 #ELSE
 ;
 DSKY_ENTRY:
-	CALL	PANIC
+	CALL	PANIC		; NO RETURN
 ;
 #ENDIF
 ;
diff --git a/Source/HBIOS/dsrtc.asm b/Source/HBIOS/dsrtc.asm
index 01d2f171..d7cbb744 100644
--- a/Source/HBIOS/dsrtc.asm
+++ b/Source/HBIOS/dsrtc.asm
@@ -241,7 +241,10 @@ DSRTC_DISPATCH:
 	JP	Z,DSRTC_SETALM	; SET ALARM 
 	DEC	A
 	JP	Z,DSRTC_DEVICE	; REPORT RTC DEVICE INFO
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOFUNC
+	OR	A
+	RET
 ;
 ; NVRAM FUNCTIONS ARE NOT AVAILABLE IN SIMULATOR
 ;
@@ -249,7 +252,10 @@ DSRTC_GETBLK:
 DSRTC_SETBLK:
 DSRTC_GETALM:
 DSRTC_SETALM:
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ; RTC GET TIME
 ;   A: RESULT (OUT), 0=OK, Z=OK, NZ=ERR
diff --git a/Source/HBIOS/fd.asm b/Source/HBIOS/fd.asm
index b35c1e73..98ff1ead 100644
--- a/Source/HBIOS/fd.asm
+++ b/Source/HBIOS/fd.asm
@@ -483,7 +483,10 @@ FD_FNTBL:
 FD_VERIFY:
 FD_FORMAT:
 FD_DEFMED:
-	CALL	PANIC			; INVALID SUB-FUNCTION
+	CALL	SYSCHK			; INVALID SUB-FUNCTION
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -555,7 +558,8 @@ FD_MEDIARETRY:
 	;LD	(HL),0			; SET TO NO MEDIA
 	LD	(IY+FD_MEDTYP),0	; SET DRIVE = NO MEDIA
 	LD	E,0
-	OR	$FF			; SIGNAL ERROR
+	LD	A,ERR_NOMEDIA		; SIGNAL ERROR
+	OR	A			; SET FLAGS
 	RET
 
 FD_TESTMEDIA:
@@ -784,7 +788,7 @@ FD_FDCRESET:
 	LD	(FCD_FDCRDY),A
 
 	; MARK ALL DRIVES AS NEEDING RECALIBRATION
-	; NOTE THAT IF THE VALUE IS CURRENT $FF,
+	; NOTE THAT IF THE VALUE IS CURRENTLY $FF,
 	; WE NEED TO LEAVE IT ALONE, SO WE 'OR' IN THE
 	; $FE TO AVOID THIS SCENARIO.
 
@@ -972,8 +976,14 @@ FD_RETRY:
 	CALL	FC_PRTRESULTS
 #ENDIF
 
+	; RETURN APPROPRIATE HBIOS ERROR
 	LD	A,(FST_RC)
-	OR	A			; OTHERWISE SET FLAGS BASED ON RC (IN A)
+	CP	FRC_NOTWRIT
+	LD	A,ERR_READONLY		; ASSUME WRITE PROTECTED ERROR
+	JR	Z,FD_RETRY1
+	LD	A,ERR_IO		; OTHERWISE I/O ERROR
+FD_RETRY1:
+	OR	A			; SET FLAGS
 	RET				; AND GIVE UP
 ;
 ;
@@ -1042,7 +1052,10 @@ FD_RUN1:
 	JR	Z,FC_WRITE
 	CP	DOP_READID
 	JR	Z,FC_READID
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOFUNC
+	OR	A
+	RET
 
 FD_RUNCHK:
 #IF (DSKYENABLE)
diff --git a/Source/HBIOS/hbios.asm b/Source/HBIOS/hbios.asm
index ce6bf8dd..a172f71d 100644
--- a/Source/HBIOS/hbios.asm
+++ b/Source/HBIOS/hbios.asm
@@ -1796,7 +1796,7 @@ HB_DISPATCH:
 	PUSH	AF
 	LD	A,(HB_STACK - HB_STKSIZ + $08)
 	CP	$FF
-	CALL	NZ,PANIC
+	CALL	SYSCHK
 	LD	A,$FF
 	LD	(HB_STACK - HB_STKSIZ + $08),A
 	POP	AF
@@ -1813,17 +1813,20 @@ HB_DISPCALL:
 	CP	BF_RTC + $10		; $20-$2F: REAL TIME CLOCK (RTC)
 	JP	C,RTC_DISPATCH
 	CP	BF_EMU + $10		; $30-$3F: EMULATION
-	CALL	C,PANIC			; OBSOLETE!
+	JR	C,HB_DISPERR
 	CP	BF_VDA + $10		; $40-$4F: VIDEO DISPLAY ADAPTER
 	JP	C,VDA_DISPATCH
-
 	CP	BF_SND + $08		; $50-$58: SOUND DRIVERS
 	JP	C,SND_DISPATCH
-
 	CP	BF_SYS			; SKIP TO BF_SYS VALUE AT $F0
-	CALL	C,PANIC			; PANIC IF LESS THAN BF_SYS
+	JR	C,HB_DISPERR		; ERROR IF LESS THAN BF_SYS
 	JP	SYS_DISPATCH		; OTHERWISE SYS CALL
-	CALL	PANIC			; THIS SHOULD NEVER BE REACHED
+	; FALL THRU
+;
+HB_DISPERR:
+	CALL	SYSCHK
+	LD	A,ERR_NOFUNC
+	OR	A
 	RET
 ;
 ;==================================================================================================
@@ -2185,7 +2188,7 @@ RTC_DISPATCH:
 	RET
 ;
 RTC_DISPERR:
-	;CALL	PANIC
+	CALL	SYSCHK
 	LD	A,ERR_NOHW
 	OR	A
 	RET
@@ -2340,7 +2343,7 @@ SYS_RESET:
 	JR	Z,SYS_RESWARM
 	CP	BF_SYSRES_COLD
 	JR	Z,SYS_RESCOLD
-	;CALL	PANIC
+	CALL	SYSCHK
 	LD	A,ERR_NOFUNC
 	OR	A			; SIGNAL ERROR
 	RET
@@ -2453,7 +2456,7 @@ SYS_ALLOC:
 ; ALL OTHER REGISTERS PRESERVED
 ;
 SYS_FREE:
-	;CALL	PANIC			; NOT YET IMPLEMENTED
+	CALL	SYSCHK			; NOT YET IMPLEMENTED
 	LD	A,ERR_NOTIMPL		; NOT YET INMPLEMENTED
 	OR	A			; SET FLAGS
 	RET
@@ -2470,9 +2473,9 @@ SYS_GET:
 	CP	BF_SYSGET_RTCCNT
 	JR	Z,SYS_GETRTCCNT
 	CP	BF_SYSGET_VDACNT
-	JR	Z,SYS_GETVDACNT
+	JP	Z,SYS_GETVDACNT
 	CP	BF_SYSGET_SNDCNT
-	JR	Z, SYS_GETSNDCNT
+	JP	Z, SYS_GETSNDCNT
 	CP	BF_SYSGET_TIMER
 	JR	Z,SYS_GETTIMER
 	CP	BF_SYSGET_SECS
@@ -2485,7 +2488,7 @@ SYS_GET:
 	JR	Z,SYS_GETMEMINFO
 	CP	BF_SYSGET_BNKINFO
 	JR	Z,SYS_GETBNKINFO
-	;CALL	PANIC
+	CALL	SYSCHK
 	LD	A,ERR_NOFUNC		; SIGNAL ERROR
 	OR	A			; SET FLAGS
 	RET
@@ -2625,7 +2628,7 @@ SYS_SET:
 	JR	Z,SYS_SETSECS
 	CP	BF_SYSSET_BOOTINFO
 	JR	Z,SYS_SETBOOTINFO
-	;CALL	PANIC
+	CALL	SYSCHK
 	LD	A,ERR_NOFUNC		; SIGNAL ERROR
 	OR	A			; SET FLAGS
 	RET
@@ -2722,7 +2725,7 @@ SYS_INT:
 	JR	Z,SYS_INTGET
 	CP	BF_SYSINT_SET
 	JR	Z,SYS_INTSET
-	;CALL	PANIC
+	CALL	SYSCHK
 	LD	A,ERR_NOFUNC		; SIGNAL ERROR
 	OR	A			; SET FLAGS
 	RET
@@ -2750,7 +2753,7 @@ SYS_INTINFO:
 ;
 SYS_INTVECADR:
 #IF (INTMODE == 0)
-	;CALL	PANIC			; INVALID FOR INT MODE 0
+	CALL	SYSCHK			; INVALID FOR INT MODE 0
 	LD	A,ERR_BADCFG		; SIGNAL ERROR
 	OR	A			; SET FLAGS
 	RET
@@ -2766,7 +2769,7 @@ SYS_INTVECADR:
 	LD	A,E			; INCOMING INDEX POSITION TO A
 	CP	C			; COMPARE TO VECTOR COUNT
 	JR	C,SYS_INTGET1		; CONTINUE IF POSITION IN RANGE
-	;CALL	PANIC			; ELSE ERROR
+	CALL	SYSCHK			; ELSE ERROR
 	LD	A,ERR_RANGE		; SIGNAL ERROR
 	OR	A			; SET FLAGS
 	RET
@@ -2985,13 +2988,13 @@ HB_DISPCALL:
 	RET				; JUMP TO DRIVER FUNC ADR ON TOS
 ;
 HB_FUNCERR:
-	;CALL	PANIC
+	CALL	SYSCHK
 	LD	A,ERR_NOFUNC		; SIGNAL ERROR
 	OR	A			; SET FLAGS
 	RET
 ;
 HB_UNITERR:
-	;CALL	PANIC
+	CALL	SYSCHK
 	LD	A,ERR_NOUNIT		; SIGNAL ERROR
 	OR	A			; SET FLAGS
 	RET
@@ -3080,7 +3083,7 @@ HB_ALLOC:
 HB_ALLOC1:
 	; ERROR RETURN
 	POP	DE			; RESTORE INCOMING DE
-	;CALL	PANIC
+	CALL	SYSCHK
 	LD	A,ERR_NOMEM		; SIGNAL ERROR
 	OR	A			; SET FLAGS
 	RET
diff --git a/Source/HBIOS/hbios.inc b/Source/HBIOS/hbios.inc
index d0734cd2..491f2422 100644
--- a/Source/HBIOS/hbios.inc
+++ b/Source/HBIOS/hbios.inc
@@ -132,6 +132,7 @@ ERR_IO			.EQU	-9	; I/O ERROR
 ERR_READONLY		.EQU	-10	; WRITE REQ TO READ-ONLY MEDIA	
 ERR_TIMEOUT		.EQU	-11	; DEVICE TIMEOUT
 ERR_BADCFG		.EQU	-12	; INVALID CONFIGURATION
+ERR_INTERNAL		.EQU	-13	; INTERNAL ERROR
 ;
 ; MEDIA ID VALUES
 ;
diff --git a/Source/HBIOS/hdsk.asm b/Source/HBIOS/hdsk.asm
index e6643dd1..1d1b3c84 100644
--- a/Source/HBIOS/hdsk.asm
+++ b/Source/HBIOS/hdsk.asm
@@ -121,7 +121,10 @@ HDSK_FNTBL:
 HDSK_VERIFY:
 HDSK_FORMAT:
 HDSK_DEFMED:
-	CALL	PANIC			; INVALID SUB-FUNCTION
+	CALL	SYSCHK			; INVALID SUB-FUNCTION
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -291,7 +294,10 @@ HDSK_RW6:
 	LD	E,C			; SECTOR READ COUNT TO E
 	LD	HL,(HDSK_DMA)		; CURRENT DMA TO HL
 	OR	A			; SET FLAGS BASED ON RETURN CODE
-	RET				; AND RETURN, A HAS RETURN CODE
+	RET	Z			; RETURN IF SUCCESS
+	LD	A,ERR_IO		; SIGNAL IO ERROR
+	OR	A			; SET FLAGS
+	RET				; AND DONE
 ;
 ;
 ;
diff --git a/Source/HBIOS/ide.asm b/Source/HBIOS/ide.asm
index 02f3d813..d6164225 100644
--- a/Source/HBIOS/ide.asm
+++ b/Source/HBIOS/ide.asm
@@ -461,7 +461,10 @@ IDE_FNTBL:
 IDE_VERIFY:
 IDE_FORMAT:
 IDE_DEFMED:
-	CALL	PANIC			; NOT IMPLEMENTED
+	CALL	SYSCHK			; NOT IMPLEMENTED
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -520,7 +523,10 @@ IDE_IO3:
 	LD	E,C			; SECTOR READ COUNT TO E
 	LD	HL,(IDE_DSKBUF)		; CURRENT DMA TO HL
 	OR	A			; SET FLAGS BASED ON RETURN CODE
-	RET				; AND RETURN, A HAS RETURN CODE
+	RET	Z			; RETURN IF SUCCESS
+	LD	A,ERR_IO		; SIGNAL IO ERROR
+	OR	A			; SET FLAGS
+	RET				; AND DONE
 ;
 ;
 ;
@@ -574,6 +580,8 @@ IDE_MEDIA2:
 	LD	E,MID_HD		; ASSUME WE ARE OK
 	RET	Z			; RETURN IF GOOD INIT
 	LD	E,MID_NONE		; SIGNAL NO MEDIA
+	LD	A,ERR_NOMEDIA		; NO MEDIA ERROR
+	OR	A			; SET FLAGS
 	RET				; AND RETURN
 ;
 ;
diff --git a/Source/HBIOS/intrtc.asm b/Source/HBIOS/intrtc.asm
index a7d05ac7..3765bf1d 100644
--- a/Source/HBIOS/intrtc.asm
+++ b/Source/HBIOS/intrtc.asm
@@ -56,7 +56,10 @@ INTRTC_DISPATCH:
 	JP	Z,INTRTC_SETALM	; SET ALARM 
 	DEC	A
 	JP	Z,INTRTC_DEVICE	; REPORT RTC DEVICE INFO
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOFUNC
+	OR	A
+	RET
 ;
 ; NVRAM FUNCTIONS ARE NOT AVAILABLE IN SIMULATOR
 ;
@@ -66,7 +69,10 @@ INTRTC_GETBLK:
 INTRTC_SETBLK:
 INTRTC_GETALM:
 INTRTC_SETALM:
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ; RTC GET TIME
 ;   A: RESULT (OUT), 0=OK, Z=OK, NZ=ERR
@@ -197,7 +203,7 @@ INTRTC_INT2:
 	JR	NZ,INTRTC_INTX		; NOPE, DONE
 	LD	(HL),0			; BACK TO YEAR ZERO
 INTRTC_INTX:
-	JP	PANIC
+	JP	SYSCHK
 INTRTC_VEC	.EQU	$-2
 ;
 ; CONVERT FROM BINARY BUF (HL) TO BCD BUF (DE)
diff --git a/Source/HBIOS/md.asm b/Source/HBIOS/md.asm
index 9d290c0a..81567653 100644
--- a/Source/HBIOS/md.asm
+++ b/Source/HBIOS/md.asm
@@ -80,7 +80,10 @@ MD_FNTBL:
 MD_VERIFY:
 MD_FORMAT:
 MD_DEFMED:
-	CALL	PANIC			; INVALID SUB-FUNCTION
+	CALL	SYSCHK			; INVALID SUB-FUNCTION
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -102,7 +105,10 @@ MD_CAP:
 	JR	Z,MD_CAP0		; UNIT 0
 	DEC	A			; TRY UNIT 1
 	JR	Z,MD_CAP1		; UNIT 1
-	CALL	PANIC			; PANIC ON INVALID UNIT
+	CALL	SYSCHK			; INVALID UNIT
+	LD	A,ERR_NOUNIT
+	OR	A
+	RET
 MD_CAP0:
 	LD	A,(HCB + HCB_ROMBANKS)	; POINT TO ROM BANK COUNT
 	JR	MD_CAP2
diff --git a/Source/HBIOS/ppide.asm b/Source/HBIOS/ppide.asm
index a15d35a5..6b795ed3 100644
--- a/Source/HBIOS/ppide.asm
+++ b/Source/HBIOS/ppide.asm
@@ -470,7 +470,10 @@ PPIDE_FNTBL:
 PPIDE_VERIFY:
 PPIDE_FORMAT:
 PPIDE_DEFMED:
-	CALL	PANIC			; NOT IMPLEMENTED
+	CALL	SYSCHK			; NOT IMPLEMENTED
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -529,7 +532,10 @@ PPIDE_IO3:
 	LD	E,C			; SECTOR READ COUNT TO E
 	LD	HL,(PPIDE_DSKBUF)	; CURRENT DMA TO HL
 	OR	A			; SET FLAGS BASED ON RETURN CODE
-	RET				; AND RETURN, A HAS RETURN CODE
+	RET	Z			; RETURN IF SUCCESS
+	LD	A,ERR_IO		; SIGNAL IO ERROR
+	OR	A			; SET FLAGS
+	RET				; AND DONE
 ;
 ;
 ;
@@ -583,6 +589,8 @@ PPIDE_MEDIA2:
 	LD	E,MID_HD		; ASSUME WE ARE OK
 	RET	Z			; RETURN IF GOOD INIT
 	LD	E,MID_NONE		; SIGNAL NO MEDIA
+	LD	A,ERR_NOMEDIA		; NO MEDIA ERROR
+	OR	A			; SET FLAGS
 	RET				; AND RETURN
 ;
 ;
@@ -978,7 +986,7 @@ PPIDE_RESET:
 	; OLDER CF CARDS DO NOT SEEM TO SET THE 
 	; REGISTERS ON RESET, SO HERE WE FAKE THINGS BY
 	; SETTING THEM AS A RESET WOULD
-#IF (IDETRACE >= 3)
+#IF (PPIDETRACE >= 3)
 	PRTS(" FAKE$")
 #ENDIF
 	XOR	A
diff --git a/Source/HBIOS/ppp.asm b/Source/HBIOS/ppp.asm
index 0b45b1eb..e564db7d 100644
--- a/Source/HBIOS/ppp.asm
+++ b/Source/HBIOS/ppp.asm
@@ -338,7 +338,10 @@ PPPCON_OST:
 ;
 ;
 PPPCON_INITDEV:
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -499,7 +502,10 @@ PPPSD_FNTBL:
 PPPSD_VERIFY:
 PPPSD_FORMAT:
 PPPSD_DEFMED:
-	CALL	PANIC			; INVALID SUB-FUNCTION
+	CALL	SYSCHK			; INVALID SUB-FUNCTION
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -566,8 +572,11 @@ PPPSD_IO2:
 PPPSD_IO3:
 	LD	E,C			; SECTOR READ COUNT TO E
 	LD	HL,(PPPSD_DSKBUF)	; CURRENT BUF ADR TO HL
+	OR	A			; SET FLAGS BASED ON RETURN CODE
+	RET	Z			; RETURN IF SUCCESS
+	LD	A,ERR_IO		; SIGNAL IO ERROR
 	OR	A			; SET FLAGS
-	RET				; RETURN WITH A = STATUS
+	RET				; AND DONE
 ;
 ;
 ;
@@ -697,6 +706,8 @@ PPPSD_MEDIA:
 	LD	E,MID_HD		; ASSUME WE ARE OK
 	RET	Z			; RETURN IF GOOD INIT
 	LD	E,MID_NONE		; SIGNAL NO MEDA
+	LD	A,ERR_NOMEDIA		; NO MEDIA ERROR
+	OR	A			; SET FLAGS
 	RET				; AND RETURN
 ;
 ;
diff --git a/Source/HBIOS/prp.asm b/Source/HBIOS/prp.asm
index bb95606f..3ed73f09 100644
--- a/Source/HBIOS/prp.asm
+++ b/Source/HBIOS/prp.asm
@@ -211,7 +211,10 @@ PRPCON_OST1:
 ;
 ;
 PRPCON_INITDEV:
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -396,7 +399,10 @@ PRPSD_FNTBL:
 PRPSD_VERIFY:
 PRPSD_FORMAT:
 PRPSD_DEFMED:
-	CALL	PANIC			; INVALID SUB-FUNCTION
+	CALL	SYSCHK			; INVALID SUB-FUNCTION
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -463,8 +469,11 @@ PRPSD_IO2:
 PRPSD_IO3:
 	LD	E,C			; SECTOR READ COUNT TO E
 	LD	HL,(PRPSD_DSKBUF)	; CURRENT BUF ADR TO HL
+	OR	A			; SET FLAGS BASED ON RETURN CODE
+	RET	Z			; RETURN IF SUCCESS
+	LD	A,ERR_IO		; SIGNAL IO ERROR
 	OR	A			; SET FLAGS
-	RET				; RETURN WITH A = STATUS
+	RET				; AND DONE
 ;
 ;
 ;
@@ -553,6 +562,8 @@ PRPSD_MEDIA:
 	LD	E,MID_HD		; ASSUME WE ARE OK
 	RET	Z			; RETURN IF GOOD INIT
 	LD	E,MID_NONE		; SIGNAL NO MEDA
+	LD	A,ERR_NOMEDIA		; NO MEDIA ERROR
+	OR	A			; SET FLAGS
 	RET				; AND RETURN
 ;
 ;
diff --git a/Source/HBIOS/rf.asm b/Source/HBIOS/rf.asm
index 2ecba90f..6fbedfe2 100644
--- a/Source/HBIOS/rf.asm
+++ b/Source/HBIOS/rf.asm
@@ -138,7 +138,10 @@ RF_FNTBL:
 RF_VERIFY:
 RF_FORMAT:
 RF_DEFMED:
-	CALL	PANIC			; INVALID SUB-FUNCTION
+	CALL	SYSCHK			; INVALID SUB-FUNCTION
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -219,7 +222,8 @@ RF_WRITE:
 	CALL	RF_CHKWP		; WRITE PROTECTED?
 	JR	Z,RF_RW			; IF 0, NOT WP, CONTINUE WITH GENERIC R/W ROUTINE
 	LD	E,0			; ZERO SECTORS WRITTEN
-	OR	$FF			; SIGNAL ERROR
+	LD	A,ERR_READONLY		; SIGNAL ERROR
+	OR	A			; SET FLAGS
 	RET				; AND DONE
 ;
 ;
@@ -255,7 +259,10 @@ RF_RW3:
 	LD	E,C			; SECTOR READ COUNT TO E
 	LD	HL,(RF_DSKBUF)		; CURRENT DMA TO HL
 	OR	A			; SET FLAGS BASED ON RETURN CODE
-	RET				; AND RETURN, A HAS RETURN CODE
+	RET	Z			; RETURN SUCCESS
+	LD	A,ERR_IO		; SIGNAL IO ERROR
+	OR	A			; SET FLAGS
+	RET				; AND DONE
 ;
 ; READ SECTOR
 ;
diff --git a/Source/HBIOS/sd.asm b/Source/HBIOS/sd.asm
index 1568942b..ce6cebf7 100644
--- a/Source/HBIOS/sd.asm
+++ b/Source/HBIOS/sd.asm
@@ -672,7 +672,10 @@ SD_FNTBL:
 SD_VERIFY:
 SD_FORMAT:
 SD_DEFMED:
-	CALL	PANIC			; INVALID SUB-FUNCTION
+	CALL	SYSCHK			; INVALID SUB-FUNCTION
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ;
 ;
@@ -737,7 +740,10 @@ SD_IO3:
 	LD	E,C			; SECTOR READ COUNT TO E
 	LD	HL,(SD_DSKBUF)		; CURRENT DMA TO HL
 	OR	A			; SET FLAGS BASED ON RETURN CODE
-	RET				; AND RETURN, A HAS RETURN CODE
+	RET	Z			; RETURN IF SUCCESS
+	LD	A,ERR_IO		; SIGNAL IO ERROR
+	OR	A			; SET FLAGS
+	RET				; AND DONE
 ;
 ;
 ;
@@ -802,6 +808,8 @@ SD_MEDIA2:
 	LD	E,MID_HD		; ASSUME WE ARE OK
 	RET	Z			; RETURN IF GOOD INIT
 	LD	E,MID_NONE		; SIGNAL NO MEDIA
+	LD	A,ERR_NOMEDIA		; NO MEDIA ERROR
+	OR	A			; SET FLAGS
 	RET				; AND RETURN
 ;
 ;
@@ -1054,10 +1062,14 @@ SD_INITCARD5:
 	; GET SIZE OF DEVICE IN BLOCKS
 	LD	A,(IY+SD_TYPE)		; GET CARD TYPE
 	OR	A			; SET FLAGS
-	CALL	Z,PANIC			; PANIC IF CARD TYPE UNKNOWN
+	JR	Z,SD_INITCARD5A		; HANDLE CARD TYPE UNKNOWN
 	CP	SD_TYPESDHC		; COMPARE TO SDHC (V2)
 	JP	NC,SD_INITCARD8		; HANDLE SDHC (V2) OR BETTER
 	JR	SD_INITCARD6		; HANDLE MMC OR SDSC
+;	
+SD_INITCARD5A:
+	CALL	SYSCHK
+	JP	SD_NOMEDIA
 ;
 ; CAPACITY CALCULATION FOR MMC OR SDSC (V1) CARDS:
 ; BYTES = (C_SIZE + 1) * 2^(2+C_SIZE_MULT+READ_BL_LEN) = (C_SIZE+1) << (2+C_SIZE_MULT+READ_BL_LEN)
@@ -1165,6 +1177,9 @@ SD_SECTIO:
 	CP	SD_CMD_WRITE_BLOCK	; WRITE_BLOCK?
 	JR	Z,SD_SECTIO2		; HANDLE WRITE
 	CALL	PANIC			; PANIC ON ANYTHING ELSE
+	LD	A,ERR_INTERNAL
+	OR	A
+	RET
 SD_SECTIO1:
 	; GET SECTOR DATA
 	CALL	SD_GETDATA		; GET THE BLOCK
diff --git a/Source/HBIOS/simrtc.asm b/Source/HBIOS/simrtc.asm
index 0185bd93..28394990 100644
--- a/Source/HBIOS/simrtc.asm
+++ b/Source/HBIOS/simrtc.asm
@@ -55,7 +55,10 @@ SIMRTC_DISPATCH:
 	JP	Z,SIMRTC_SETALM	; SET ALARM 
 	DEC	A
 	JP	Z,SIMRTC_DEVICE	; REPORT RTC DEVICE INFO
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOFUNC
+	OR	A
+	RET
 ;
 ; NVRAM FUNCTIONS ARE NOT AVAILABLE IN SIMULATOR
 ;
@@ -65,7 +68,10 @@ SIMRTC_GETBLK:
 SIMRTC_SETBLK:
 SIMRTC_GETALM:
 SIMRTC_SETALM:
-	CALL	PANIC
+	CALL	SYSCHK
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 ;
 ; RTC GET TIME
 ;   A: RESULT (OUT), 0=OK, Z=OK, NZ=ERR
diff --git a/Source/HBIOS/sio.asm b/Source/HBIOS/sio.asm
index 631cb605..9d7fc13a 100644
--- a/Source/HBIOS/sio.asm
+++ b/Source/HBIOS/sio.asm
@@ -839,7 +839,10 @@ SIO_INITGO:
 	LD	L,SIO1_VEC		; ASSUME CHIP 1
 	DEC	A			; CHIP 1?
 	JR	Z,SIO_INITIVT		; IF SO, DO IT
-	CALL 	PANIC			; IMPOSSIBLE SITUATION
+	CALL 	SYSCHK			; IMPOSSIBLE SITUATION
+	LD	A,ERR_NOUNIT
+	OR	A
+	RET
 SIO_INITIVT:
 	LD	A,L			; VALUE TO A
 	LD	(SIO_WR2),A		; SAVE IT
diff --git a/Source/HBIOS/std.asm b/Source/HBIOS/std.asm
index b62a6486..a6ee8022 100644
--- a/Source/HBIOS/std.asm
+++ b/Source/HBIOS/std.asm
@@ -30,6 +30,10 @@ USEXIO		.EQU	1		; BASIC SERIAL DRIVER
 USEMIO		.EQU	2		; MEMORY BUFFER DRIVER
 WBWDEBUG	.EQU	USENONE
 ;
+; DISPLAY SYSTEM CHECKS?
+;
+SYSCHKENABLE	.EQU	FALSE
+;
 ; PRIMARY HARDWARE PLATFORMS
 ;
 PLT_SBC		.EQU	1		; SBC ECB Z80 SBC
diff --git a/Source/HBIOS/tms.asm b/Source/HBIOS/tms.asm
index fb594f93..6fae1b9b 100644
--- a/Source/HBIOS/tms.asm
+++ b/Source/HBIOS/tms.asm
@@ -224,7 +224,10 @@ TMS_VDADEV:
 	RET
 
 TMS_VDASCS:
-	CALL	PANIC		; NOT IMPLEMENTED (YET)
+	CALL	SYSCHK		; NOT IMPLEMENTED (YET)
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 
 TMS_VDASCP:
 #IF (CPUFAM == CPU_Z180)
diff --git a/Source/HBIOS/util.asm b/Source/HBIOS/util.asm
index 8dc066db..7a8868dd 100644
--- a/Source/HBIOS/util.asm
+++ b/Source/HBIOS/util.asm
@@ -381,17 +381,30 @@ TSTPT:
 	POP	DE
 	JR	REGDMP			; DUMP REGISTERS AND RETURN
 ;
-; PANIC: TRY TO DUMP MACHINE STATE
+; SYSTEM CHECK: DUMP MACHINE STATE AND CONTINUE?
 ;
-PANIC:
+SYSCHK:
+#IF (SYSCHKENABLE)
 	PUSH	DE
-	LD	DE,STR_PANIC
+	LD	DE,STR_SYSCHK
 	CALL	WRITESTR
 	POP	DE
 	CALL	XREGDMP			; DUMP REGISTERS
 	CALL	CONTINUE		; CHECK W/ USER
+#ENDIF
 	RET
 ;
+; PANIC: DUMP MACHINE STATE AND HALT
+;
+PANIC:
+	PUSH	DE
+	LD	DE,STR_PANIC
+	CALL	WRITESTR
+	POP	DE
+	CALL	XREGDMP			; DUMP REGISTERS
+	DI				; NO INTERRUPTS
+	HALT				; FULL STOP
+;
 ;
 ;
 REGDMP:
@@ -504,6 +517,7 @@ CONTINUE3:
 ;
 ;
 STR_PANIC	.DB	"\r\n\r\n>>> PANIC: $"
+STR_SYSCHK	.DB	"\r\n\r\n>>> SYSCHK: $"
 STR_TSTPT	.TEXT	"\r\n+++ TSTPT: $"
 STR_CONTINUE	.TEXT	" Continue? (Y/N): $"
 ;STR_AF		.DB	" AF=$"
diff --git a/Source/HBIOS/vga.asm b/Source/HBIOS/vga.asm
index 30bb2b4e..dde3ae33 100644
--- a/Source/HBIOS/vga.asm
+++ b/Source/HBIOS/vga.asm
@@ -208,7 +208,10 @@ VGA_VDADEV:
 	RET
 
 VGA_VDASCS:
-	CALL	PANIC		; NOT IMPLEMENTED (YET)
+	CALL	SYSCHK		; NOT IMPLEMENTED (YET)
+	LD	A,ERR_NOTIMPL
+	OR	A
+	RET
 
 VGA_VDASCP:
 	CALL	VGA_XY		; SET CURSOR POSITION
diff --git a/Source/ver.inc b/Source/ver.inc
index 863b88bf..74eae58b 100644
--- a/Source/ver.inc
+++ b/Source/ver.inc
@@ -2,4 +2,4 @@
 #DEFINE	RMN	1
 #DEFINE	RUP	1
 #DEFINE	RTP	0
-#DEFINE BIOSVER	"3.1.1-pre.10"
+#DEFINE BIOSVER	"3.1.1-pre.11"
diff --git a/Source/ver.lib b/Source/ver.lib
index d8f586c1..f0a72730 100644
--- a/Source/ver.lib
+++ b/Source/ver.lib
@@ -3,5 +3,5 @@ rmn	equ	1
 rup	equ	1
 rtp	equ	0
 biosver	macro
-	db	"3.1.1-pre.10"
+	db	"3.1.1-pre.11"
 	endm