Resident driver template — joystick + keypad

Updated 7 Sep 2026

← All Voltmace Delta 14B Driver versions

This disassembly

Install the resident joystick driver

Point BYTEV at the OSBYTE intercept at &0A0D. Called from the BASIC via CALL &A00, after it has saved the previous BYTEV (line 50) and patched the chain slot (line 1840) and sensitivity thresholds (line 1850). Preserves A (saved and restored); X and Y are untouched.

On Exit	A	preserved
	X	preserved
	Y	preserved

0A00

.install

PHA ; Preserve A

0A01

LDA #&0d ; BYTEV low byte -> &0D...

0A03

STA bytev ; store it

0A06

LDA #&0a ; ...high byte -> &0A...

0A08

STA bytev_hi ; ...so every OSBYTE now enters the handler at &0A0D

0A0B

PLA ; Restore A

0A0C

RTS ; Return to the BASIC caller

BYTEV handler: map the joystick and keypad to INKEY As variant A, but joystick_map entries >= &10 test the Delta 14B keypad matrix through the User VIA instead of an analogue channel.
0A0D	.osbyte_intercept
	CMP #osbyte_inkey ; Only intercept OSBYTE &81 (INKEY / read key)
0A0F	BNE chain ; other reason codes -> chain to the previous handler
0A11	PHA ; Preserve A (reason code)...
0A12	TYA ; Preserve Y (INKEY high byte)...
0A13	PHA ; on the stack
0A14	TXA ; A := X = the INKEY key number being tested
0A15	PHA ; ...(X also preserved)
0A16	LDY #0 ; No match yet...
0A18	STY result_flag ; ...clear the result flag
0A1B	.scan_map←1← 0A27 BNE
	CMP joystick_map,y ; Does the tested key match this map entry?
0A1E	BNE scan_next ; no -> skip it
0A20	JSR read_input ; yes -> read the mapped input for it
0A23	.scan_next←1← 0A1E BNE
	INY ; Step over the 2-byte entry...
0A24	INY ; twice
0A25	CPY #&48 ; end of the map?
0A27	BNE scan_map ; no -> keep scanning
0A29	LDA result_flag ; Did any mapped input read as active?
0A2C	BEQ not_pressed ; no -> return the normal INKEY result
0A2E	TAX ; yes: return "key pressed" (X=Y=&FF)...
0A2F	TAY ; X and Y
0A30	PLA ; drop the saved X...
0A31	PLA ; ...Y...
0A32	PLA ; ...A
0A33	RTS ; and return, claiming the OSBYTE
0A34	.not_pressed←1← 0A2C BEQ
	PLA ; Restore X...
0A35	TAX ; into X
0A36	PLA ; Restore Y...
0A37	TAY ; into Y
0A38	PLA ; Restore A
0A39	.chain←1← 0A0F BNE
	JMP chain_to_old_bytev ; Pass the call to the previous BYTEV (chain slot below)

Test one joystick or keypad input

For the matched entry: entries below &10 read an analogue channel (OSBYTE &80 / ADVAL) against the thresholds; entries >= &10 strobe a keypad column through User VIA port B and test a row bit. A hit sets result_flag. Preserves A and Y (Y is the caller's map-scan index) but corrupts X.

On Exit	A	preserved
	Y	preserved
	X	corrupted

0A3C

.read_input←1

PHA ; Preserve A...

0A3D

TYA ; Preserve Y...

0A3E

PHA ; on the stack

0A3F

CMP #&10 ; Analogue entry (< &10) or keypad entry?

0A41

BPL test_keypad ; >= &10 -> the keypad path

0A43

INY ; Point at the entry parameter

0A44

LDA joystick_map,y ; ADC channel in the top nibble...

0A47

LSR ; ...shift it down...

0A48

LSR ; ...shift it down...

0A49

LSR ; ...shift it down...

0A4A

LSR ; ...shift it down...

0A4B

TAX ; ...into X for OSBYTE &80

0A4C

LDA joystick_map,y ; reload the parameter

0A4F

AND #1 ; low bit picks which threshold (push vs pull)

0A51

BEQ test_high_threshold ; else test the high threshold

0A53

LDA #osbyte_read_adc_or_get_buffer_status ; OSBYTE &80: read ADC channel X (ADVAL, Y=high byte)...

0A55

JSR osbyte ; call OSBYTE Read ADC channel X or buffer status

0A58

CPY threshold_lo ; past the low threshold?

0A5B

BCC read_done ; no -> not active

0A5D

BCS active ; yes -> active

0A5F

.test_high_threshold←1

LDA #osbyte_read_adc_or_get_buffer_status ; OSBYTE &80: read ADC channel X...

0A61

JSR osbyte ; call OSBYTE Read ADC channel X or buffer status

0A64

CPY threshold_hi ; past the high threshold?

0A67

BCC active ; no -> active

0A69

BCS read_done ; yes -> not active

0A6B

.test_keypad←1

INY ; Point at the entry parameter

0A6C

LDA joystick_map,y ; top nibble = the column strobe...

0A6F

AND #&f0 ; mask the top nibble

0A71

STA col_strobe ; ...saved

0A74

LDA joystick_map,y ; low nibble = the row bit mask...

0A77

AND #&0f ; mask the low nibble

0A79

LDY #&f0 ; DDRB = &F0: strobes out, rows in...

0A7B

STY user_via_ddrb ; set it

0A7E

STA row_mask ; save the row mask

0A81

LDY col_strobe ; Drive the column strobe...

0A84

STY user_via_orb_irb ; ...onto port B

0A87

LDY user_via_orb_irb ; Read the rows back...

0A8A

TYA ; into A

0A8B

AND row_mask ; ...and mask this row bit

0A8E

BEQ active ; low (pressed) -> not-active path...

0A90

BNE read_done ; high -> active

0A92

.active←3

LDA #&ff ; Flag a hit...

0A94

STA result_flag ; ...in result_flag

0A97

.read_done←3

PLA ; Restore Y...

TAY ; into Y

PLA ; Restore A

RTS ; Done

.row_mask←2

EQUB &EA ; Scratch: keypad row bit mask (&EA at rest)

0A9C

.col_strobe←2

EQUB &EA ; Scratch: keypad column strobe (&EA at rest)

0A9D

.result_flag←3

EQUB &EA ; Result byte (&EA at rest): the handler zeroes it, then sets it to &FF if a mapped input reads active

; Unused

0A9E

.unused_b

EQUB &00, &00, &00, &00, &00, &00, &00, &00, &00, &00, &00, &00, &00, &00, &00, &00, &00, &00

; 2-byte entries <INKEY key, input descriptor>. The key byte is ; 0 here; the BASIC (PROCASSEM, lines 1780-1830) pokes each with ; the user's chosen INKEY value. The fixed descriptor decodes ; as:

0AB0

.joystick_map←5

EQUB &00, ; joystick axis: ADC channel 1, high threshold &10

0AB2

EQUB &00, &11 ; joystick axis: ADC channel 1, low threshold

0AB4

EQUB &00, ; joystick axis: ADC channel 2, high threshold &20

0AB6

EQUB &00, &21 ; joystick axis: ADC channel 2, low threshold

0AB8

EQUB &00, ; joystick axis: ADC channel 3, high threshold &30

0ABA

EQUB &00, &31 ; joystick axis: ADC channel 3, low threshold

0ABC

EQUB &00, ; joystick axis: ADC channel 4, high threshold &40

0ABE

EQUB &00, &41 ; joystick axis: ADC channel 4, low threshold

0AC0

EQUB &00, &51 ; keypad: strobe column &50, test row bit &1

0AC2

EQUB &00, &51 ; keypad: strobe column &50, test row bit &1

0AC4

EQUB &00, &51 ; keypad: strobe column &50, test row bit &1

0AC6

EQUB &00, &31 ; keypad: strobe column &30, test row bit &1

0AC8

EQUB &00, &61 ; keypad: strobe column &60, test row bit &1

0ACA

EQUB &00, &32 ; keypad: strobe column &30, test row bit &2

0ACC

EQUB &00, &52 ; keypad: strobe column &50, test row bit &2

0ACE

EQUB &00, &62 ; keypad: strobe column &60, test row bit &2

0AD0

EQUB &00, &34 ; keypad: strobe column &30, test row bit &4

0AD2

EQUB &00, &54 ; keypad: strobe column &50, test row bit &4

0AD4

EQUB &00, &64 ; keypad: strobe column &60, test row bit &4

0AD6

EQUB &00, &38 ; keypad: strobe column &30, test row bit &8

0AD8

EQUB &00, &58 ; keypad: strobe column &50, test row bit &8

0ADA

EQUB &00, &68 ; keypad: strobe column &60, test row bit &8

0ADC

EQUB &00, &D1 ; keypad: strobe column &D0, test row bit &1

0ADE

EQUB &00, &D1 ; keypad: strobe column &D0, test row bit &1

0AE0

EQUB &00, &D1 ; keypad: strobe column &D0, test row bit &1

0AE2

EQUB &00, &B1 ; keypad: strobe column &B0, test row bit &1

0AE4

EQUB &00, &E1 ; keypad: strobe column &E0, test row bit &1

0AE6

EQUB &00, &B2 ; keypad: strobe column &B0, test row bit &2

0AE8

EQUB &00, &D2 ; keypad: strobe column &D0, test row bit &2

0AEA

EQUB &00, &E2 ; keypad: strobe column &E0, test row bit &2

0AEC

EQUB &00, &B4 ; keypad: strobe column &B0, test row bit &4

0AEE

EQUB &00, &D4 ; keypad: strobe column &D0, test row bit &4

0AF0

EQUB &00, &E4 ; keypad: strobe column &E0, test row bit &4

0AF2

EQUB &00, &B8 ; keypad: strobe column &B0, test row bit &8

0AF4

EQUB &00, &D8 ; keypad: strobe column &D0, test row bit &8

0AF6

EQUB &00, &E8 ; keypad: strobe column &E0, test row bit &8

0AF8

EQUB &00, &00 ; end-of-map marker

; RTS placeholder; the BASIC (line 1840) patches this to JMP ; <previous BYTEV> so non-INKEY OSBYTEs are chained.

0AFA

.chain_to_old_bytev←1

EQUB &60, &00, &00

0AFD

.threshold_lo←1

EQUB &00 ; Low-threshold comparison value; BASIC line 1850 pokes SH% here

0AFE

.threshold_hi←1

EQUB &00 ; High-threshold comparison value; BASIC line 1850 pokes SL% here

0AFF

.unused_b_end

EQUB &00 ; Unused

Resident driver template — joystick + keypad

This disassembly

Install the resident joystick driver

BYTEV handler: map the joystick and keypad to INKEY

Test one joystick or keypad input