diff --git a/tester-adc-sbc.mac b/tester-adc-sbc.mac
new file mode 100644
index 0000000..92fd44a
--- /dev/null
+++ b/tester-adc-sbc.mac
@@ -0,0 +1,44 @@
+.EXTERN ALL
+
+test_adc:
+; initial value
+	MOV	#32769.,R0
+; number of additions
+	MOV	#257.,R1
+
+test_adc_loop:
+	ADD	#1003.,R0
+	ADC	R0
+
+	DEC	R1
+	TST	R1
+	BNE	test_adc_loop
+
+	CMP	#28400.,R0
+	BNE	test_adc_failed
+
+; test 8 bit
+	MOV	#32769.,R0
+	MOV	#257.,R1
+
+test_adc_loop8b:
+	ADD	#13.,R0
+	ADCB	R0
+
+	DEC	R1
+	TST	R1
+	BNE	test_adc_loop8b
+
+	CMP	#36110.,R0
+	BNE	test_adc_failed
+
+	RET
+
+test_adc_failed:
+	MOV	#adc_fail_text,R0
+	CALL	print_start
+	RET
+	
+adc_fail_text:
+	.ASCII	"ADC handling FAIL\r\n\x00"
+.EVEN
diff --git a/tester.mac b/tester.mac
index f2ee34a..c8c216c 100644
--- a/tester.mac
+++ b/tester.mac
@@ -11,6 +11,7 @@ start:	MOV	#1000, R6
 	JMP	go
 
 .INCLUDE "tester-psw.mac"
+.INCLUDE "tester-adc-sbc.mac"
 
 go:	MOV	#textstart, R0
 	CALL	print_start
@@ -19,6 +20,8 @@ go:	MOV	#textstart, R0
 
 	CALL	psw_flags_trigger
 
+	CALL	test_adc
+
 	MOV	#textfin, R0
 	CALL	print_start
 	TRAP	7
@@ -52,11 +55,11 @@ print_binary:
 	MFPS	-(SP)
 	MOV	R0,-(SP)
 	MOV	R1,-(SP)
-; 8 bits in a byte
-	MOV	#8.,R1
+; 16 bits in a word
+	MOV	#16.,R1
 
 print_bit:
-	ASLB	R0
+	ASL	R0
 	BCS	print_1
 waittx0:
 	TSTB	@#TTYST