diff --git a/src/dos_m65/sdcard/sdcard_init.s b/src/dos_m65/sdcard/sdcard_init.s
index c67fdc08..9ed9878d 100644
--- a/src/dos_m65/sdcard/sdcard_init.s
+++ b/src/dos_m65/sdcard/sdcard_init.s
@@ -72,7 +72,7 @@ sdcard_init_sdsc:
 
 	lda #$00
 	sta CARD_IS_SDHC
-	lda #$40                           ; use byte addressing
+	lda #CARD_CMD_SDHC_OFF             ; $40 - use byte addressing
 	sta SD_CTL
 
 	; FALLTROUGH
@@ -111,7 +111,7 @@ sdcard_init_read:
 
 	; Trigger read
 
-	lda #$02
+	lda #CARD_CMD_READ                 ; $02
 	sta SD_CTL
 
 	; Wait for result
diff --git a/src/dos_m65/sdcard/sdcard_readsector.s b/src/dos_m65/sdcard/sdcard_readsector.s
index 14c595e7..023bf1b8 100644
--- a/src/dos_m65/sdcard/sdcard_readsector.s
+++ b/src/dos_m65/sdcard/sdcard_readsector.s
@@ -38,7 +38,7 @@ sdcard_readsector_try_loop:
 
 	; Read command
 
-	lda #$02
+	lda #CARD_CMD_READ                 ; $02
 	sta SD_CTL
 
 	; Wait for command completion
diff --git a/src/dos_m65/sdcard/sdcard_reset.s b/src/dos_m65/sdcard/sdcard_reset.s
index 29b22610..244233bf 100644
--- a/src/dos_m65/sdcard/sdcard_reset.s
+++ b/src/dos_m65/sdcard/sdcard_reset.s
@@ -9,11 +9,11 @@
 
 sdcard_reset:
 
-	ldx #$40
+	ldx #CARD_CMD_SDHC_OFF   ; $40
 	stx SD_CTL
-	ldy #$00
+	ldy #CARD_CMD_RESET      ; $00
 	sty SD_CTL
-	iny ; $01
+	ldy #CARD_CMD_END_RESET  ; $01
 	sty SD_CTL
 
 	; Wait till SD card resets
@@ -26,7 +26,7 @@ sdcard_reset:
 	
 	bit CARD_IS_SDHC
 	bpl @2
-	inx ; $41
+	ldx #CARD_CMD_SDHC_ON    ; $41
 	stx SD_CTL
 @2:
 	rts
diff --git a/src/dos_m65/sdcard/sdcard_writesector.s b/src/dos_m65/sdcard/sdcard_writesector.s
index f6ef24ae..180f198f 100644
--- a/src/dos_m65/sdcard/sdcard_writesector.s
+++ b/src/dos_m65/sdcard/sdcard_writesector.s
@@ -17,9 +17,9 @@ sdcard_writesector:
 	and #$03
 	bne sdcard_writesector             ; XXX add a timer here
 
-	; End reset XXX should this be done for sector reading too?
+	; End reset XXX is this needed? should this be done for sector reading too?
 
-	lda #$01
+	lda #CARD_CMD_END_RESET            ; $01
 	sta SD_CTL
 
 	; Set write address