diff --git a/vt.equ.S b/vt.equ.S
index fa23add..3983dd6 100644
--- a/vt.equ.S
+++ b/vt.equ.S
@@ -36,6 +36,7 @@ DECOM	ds 2 ; origin
 DECSCNM ds 2 ; screen mode
 DECAWM	ds 2 ; wrap
 DECARM	ds 2 ; auto repeat
+DECCOLM ds 2 ; character per line (80/132)
 
 
 LNM	ds 2 ; new line
@@ -46,7 +47,6 @@ SGR	ds 2 ; graphics, bit 1 = bold, 4 = underscore, 5 = blink, 7 = inverse
 *CHARSET	ds 2 ; 
 *GRAPHICS	ds 2 ; 
 
-*DECCOLM ds 2 ; character per line (80/132)
 *DECINLM ds 2 ; interlace
 *DECSCLM ds 2 ; scroll mode
 
diff --git a/vt100.cda.S b/vt100.cda.S
index 7cede82..374139d 100644
--- a/vt100.cda.S
+++ b/vt100.cda.S
@@ -284,6 +284,7 @@ variables
 	jsr decawm
 	jsr decarm
 	jsr decscnm
+	jsr deccolm
 	jsr lnm
 	jsr sgr
 	jsr dectm
@@ -384,11 +385,22 @@ decscnm
 :str	asc "DECSCNM: ",00
 
 
-lnm
+deccolm
 	mx %10
 	ldy #line_12+4
 	ldx #:str
 	jsr print_xy_str
+	lda DPAGE+DECCOLM
+	jmp print_on_off
+
+:str	asc "DECCOLM: ",00
+
+
+lnm
+	mx %10
+	ldy #line_13+4
+	ldx #:str
+	jsr print_xy_str
 	lda DPAGE+LNM
 	jmp print_on_off
 
@@ -397,7 +409,7 @@ lnm
 
 sgr
 	mx %10
-	ldy #line_13+4
+	ldy #line_14+4
 	ldx #:str
 	jsr print_xy_str
 	lda DPAGE+SGR
@@ -408,7 +420,7 @@ sgr
 
 dectm
 	mx %10
-	ldy #line_14+4
+	ldy #line_15+4
 	ldx #:str
 	jsr print_xy_str
 	lda DPAGE+DECTM
@@ -419,7 +431,7 @@ dectm
 
 decbm
 	mx %10
-	ldy #line_15+4
+	ldy #line_16+4
 	ldx #:str
 	jsr print_xy_str
 	lda DPAGE+DECBM
@@ -431,7 +443,7 @@ decbm
 
 decx
 	mx %10
-	ldy #line_16+4
+	ldy #line_17+4
 	ldx #:str
 	jsr print_xy_str
 	lda DPAGE+x
@@ -443,7 +455,7 @@ decx
 
 decy
 	mx %10
-	ldy #line_17+4
+	ldy #line_18+4
 	ldx #:str
 	jsr print_xy_str
 	lda DPAGE+y
diff --git a/vt100.csi.S b/vt100.csi.S
index 1c20abb..48e0f41 100644
--- a/vt100.csi.S
+++ b/vt100.csi.S
@@ -354,7 +354,7 @@ mode_common
 	dw :rts ; error
 	dw mode_DECCKM
 	dw mode_DECANM
-	dw :rts ; DECCOLM
+	dw mode_DECCOLM ; DECCOLM
 	dw :rts ; DECSCLM
 	dw mode_DECSCNM
 	dw mode_DECOM
@@ -396,10 +396,33 @@ mode_DECANM
 :rts	rts
 
 
-*mode_DECCOLM
-*	sty DECCOLM
-*	rts
+mode_DECCOLM
+* 80/132 mode.
+* vt102 guide states:
+* NOTE: When you change the number of columns per line, the screen is erased. 
+* This also sets the scrolling region for full screen (24 lines).
+*
+* based on testing, this always clears the screen and resets x/y, regardless of current mode.
+*
 
+	bit pmod
+	bpl :rts
+
+	sty DECCOLM
+
+	lda #0
+	sta DECTM
+	lda #23
+	sta DECBM
+	stz x
+	stz y
+
+	phy
+	jsr recalc_cursor
+	jsr erase_screen_2
+	ply
+
+:rts	rts
 
 mode_DECSCNM
 	bit pmod