Parallel ASCII Keyboard USB driver

A virtual serial port driver for a 7-bit ASCII keyboard.

Purpose

This project represents a compromise in converting old keyboards to USB. When a keyboard only sends ASCII characters, emulating a PC keyboard is a bit pointless, since there are no modifier or function keys and no key up transitions.

For a typing test, connect a terminal program. For instance, on Linux,

cu -l /dev/ttyACM0 -s 115200

Keyboards

This project was originally designed for the Micro Switch SW-series keyboard described below.

But it should work for a variety of keyboards that send ASCII characters via a parallel interface with a strobe line. These were used in early hobbyist computers, including the original Apple (see below).

Hardware

The board needs a lot of GPIO pins, particularly all of PORTB, so an actual Arduino is not a great choice.

• Teensy 2.0.
• Adafruit Atmega32u4 breakout (discontinued).
• Pololu A-Star 32U4 Mini SV.

Connections

Required:

Signal	AVR
STROBE	PD0
CHAR BIT 1	PB0
CHAR BIT 2	PB1
CHAR BIT 3	PB2
CHAR BIT 4	PB3
CHAR BIT 5	PB4
CHAR BIT 6	PB5
CHAR BIT 7	PB6

Optional:

Signal	AVR
DIRECT KEY 1	PD1
DIRECT KEY 2	PD2
...
DIRECT KEY 7	PD7
DIRECT KEY 8	PF0
DIRECT KEY 9	PF1
...
BELL	PC6
READY ACK	PC7

The rest of port D is read for direct keys. Currently the only supported actions for these are HERE IS, which sends the answerback sdtring, and BREAK, which does serial break.

There are two optional signals in the to-keyboard direction. C6 is a bell, either a speaker / transducer directly or something with a trigger signal. C7 is a ready / ack line, which can be used to time a REPEAT key or to let the keyboard track serial DTR.

Micro Switch SW-11234

A scan of the hardware documentation that came with this keyboard can be found in the wiki.

This keyboard is mostly the same as the NCR one in the Computer History Museum, except it has Ñ instead of semicolon and a few other characters moved as a result.

The state of the control and shift keys is also available separately, so it would be possible to recover more of the key state from the 7-bit character. But, really, there aren't enough keys for this to be a modern keyboard.

The microcontroller is labeled SW-20306 and is, I believe, a masked ROM version of some AMI 4-bit MCU from the 70s. It is CMOS and Vcc is -12V DC. Vdd is +5V DC, for the control signals, both inputs from the Hall Effect switches and character output. A DC-DC isolating converter like the Mornsun B0512S-1W seems to work fine.

Connections

PCB	Signal	AVR
2	-12V
3	+5V	+5V
4	GND	GND
10	/CONTROL	PD3
12	/SHIFT	PD1
A	/STROBE	PD0
C	+5V	+5V
D	GND	GND
F	CHAR BIT 2	PB1
H	CHAR BIT 1	PB0
J	CHAR BIT 4	PB3
K	CHAR BIT 3	PB2
L	CHAR BIT 5	PB4
M	CHAR BIT 6	PB5
N	CHAR BIT 7	PB6

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"SW-11234 Keyboard\"" \
  -DDIRECT_KEYS=3 -DDIRECT_PORT_UNUSED=4 -DDIRECT_INVERT_MASK=5

Micro Switch SW-11769

The same switches and keycaps as the previous, in a similar layout. Uses only 5V logic. Again control and shift keys is also available separately,

The board I tested had some hand-modifications.

Connections

PCB	Signal	AVR
3	+5V	+5V
4	GND	GND
5	CTRL	PD2
A	STROBE	PD0
C	+5V	+5V
D	GND	GND
E	SHIFT	PD1
F	CHAR BIT 2	PB1
H	CHAR BIT 1	PB0
J	CHAR BIT 4	PB3
K	CHAR BIT 3	PB2
L	CHAR BIT 5	PB4
M	CHAR BIT 6	PB5
N	CHAR BIT 7	PB6

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"SW-11769 Keyboard\"" \
  -DCONTROL_STROBE_TRIGGER=TRIGGER_RISING -DDIRECT_KEYS=2

Micro Switch SD-16234

This PCB seems to have been used in a variety of keyboards. The one I tested as a 99SD24-3.

Connection to the keyboard is through a 34-pin IDC connector.

Connections

Needed for this:

IDC	Signal	AVR
1,2,
3,4,5	GND	GND
33,34
19,20	+5V	+5V
22	/STROBE	PD0
10	CHAR BIT 1	PB0
8	CHAR BIT 2	PB1
7	CHAR BIT 3	PB2
9	CHAR BIT 4	PB3
11	CHAR BIT 5	PB4
13	CHAR BIT 6	PB5
15	CHAR BIT 7	PB6
17	CHAR BIT 8	PB7

Additional signals on this board not needed here:

IDC	Signal
12	Jumper 38 (open)
14	Jumper 34 (open)
12	Jumper 30 (open)
21	Optocoupled transistor (E)
23	Optocoupled transistor (C)
25	RESET
27	INT
29	RD
31	PSEN
24	LED (not populated)
26	LED
28	LED
30	LED
32	LED

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"SD-16234 Keyboard\"" -DCHAR_MASK=0xFF

Micro Switch SD-16534

This PCB is used at least on 91SD30-3, which seems to be part of a Honeywell BKBD terminal.

Connection to the keyboard is through a DB-25 (with a special cable not all of whose signals are connected, though there would be no harm if they were).

Connections

Needed for this:

IDC	Signal	AVR
6,7,8
9	GND	GND
10,11
12,13	+5V	+5V
4	STROBE	PD0
19	CHAR BIT 1	PB0
20	CHAR BIT 2	PB1
18	CHAR BIT 3	PB2
17	CHAR BIT 4	PB3
16	CHAR BIT 5	PB4
15	CHAR BIT 6	PB5
14	CHAR BIT 7	PB6
23	CHAR BIT 8	PB7
21	/DATA SET READY	PC7
2	SPEAKER	PC6*

Note that the two low bits are reversed from what one might expect.

The DSR line can just be wired low. If connected to PC7 and READY_ACK_MODE is defined as READY_ACK_MODE_DTR, it will be turned on as part of initialization, which causes the keyboard to send some kind of identification sequence.

The speaker connection should have a current-limiting resistor.

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"SD-16534 Keyboard\"" \
  -DCONTROL_STROBE_TRIGGER=TRIGGER_RISING -DCHAR_MASK=0xFF \
  -DREADY_ACK_MODE=READY_ACK_MODE_DTR -DREADY_ACK_ON_STATE=READY_ACK_ON_LOW

Non-ASCII Variant

A very similar PCB, SD-16604, used on 108SD30-4, from a related terminal, has the same connections, with these direct switches:

| 23 | /BREAK | PB7 | | 25 | /SHIFT | PD1 | | 24 | /CAPS LOCK | PD2 | | 1 | /CTRL | PD3 | | 5 | /AUTO LF | PD4 | | 22 | /LOCAL | PD5 |

However, the parallel signal on this board is the key number, left-to-right, top-to-bottom, and not ASCII, and unchanged for the shifts.

PARALLEL_KBD_OPTS = -DKEYBOARD="\"SD-16604 Keyboard\"" \
  -DCONTROL_STROBE_TRIGGER=TRIGGER_RISING -DBELL_MODE=BELL_MODE_TONE \
  -DDIRECT_KEYS=5 -DDIRECT_INVERT_MASK=0x1F \
  -DREADY_ACK_MODE=READY_ACK_MODE_DTR -DREADY_ACK_ON_STATE=READY_ACK_ON_LOW \
  -DDEBUG_ACTIONS

Micro Switch SC-15142

This PCB is used at least on 63ST13-1, which seems to be part of a printing terminal, with firmware SD-03041.

Connection to the keyboard is through a 20-pin IDC shrouded header.

Connections

IDC	Signal	AVR
1	DEBOUNCE(?)	PD3
4	CHAR PARITY BIT	PB7
5	/BRK	PD2
6	INPUT(?)	PC7
7	/HERE IS	PD1
8	CHAR BIT 1	PB0
10	CHAR BIT 2	PB1
11	STROBE	PD0
12	CHAR BIT 3	PB2
13,15	+5V	+5V
14,16	GROUND	GND
17	CHAR BIT 7	PB6
18	CHAR BIT 4	PB3
19	CHAR BIT 6	PB5
20	CHAR BIT 5	PB4

The third direct signal seems to change several times for each key press.

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"SC-15142 Keyboard\"" \
  -DCONTROL_STROBE_TRIGGER=TRIGGER_RISING -DPARITY_CHECK=PARITY_ODD \
  -DDIRECT_KEYS=3 -DDIRECT_INVERT_MASK=7 -DENABLE_SOF_EVENTS -DDIRECT_DEBOUNCE=5 \
  -DDIRECT_KEY_1=DIRECT_HERE_IS -DDIRECT_KEY_2=DIRECT_BREAK

Micro Switch SD-16192

This PCB is used on 78SD12-6, a terminal for the AM International AMText word processor. But many of the key legends do not match the character sent. This could be because it is used elsewhere or just due to the encoder chip.

Has an 20-pin edge connector.

Connections

IDC	Signal	AVR
A	CHAR BIT 0	PB0
B	CHAR BIT 1	PB1
C	CHAR BIT 2	PB2
D	CHAR BIT 3	PB3
E	CHAR BIT 4	PB4
F	CHAR BIT 5	PB5
H	CHAR BIT 6	PB6
J	CHAR BIT 7	PB7
K	DIRECT KEY 2	PD2
L	DIRECT KEY 3	PD3
1	DIRECT KEY 4	PD4
2	/STROBE	PD0
3	STROBE
4	-12V
5	TEST POINT P5
6	DIRECT KEY 1 (RESET)	PD1
7,8	+5V	VCC
9,10	GROUND	GND

Most keys are 4B3B, 2.5 oz. sink pulse. The RESET key in the lower-left is 4B8B, 8.0 oz., but still a pulse, which is close to synchronized with the STROBE pulse. The three keys in the upper-right are 4B3K, timed repeat, so those signals remain on while the key is still pressed. All these direct keys also send a unique character code, so other than auto-repeat there is nothing gained by tracking them separately.

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"SD-16234 Keyboard\"" -DCHAR_MASK=0xFF \
  -DDIRECT_KEYS=4 -DDIRECT_INVERT_MASK=0xF -DDIRECT_KEY_1=DIRECT_BREAK

Digital LK01

This is the main keyboard inside the VT05 display terminal and the LA32 printing terminal.

It comes in two variants. The earlier one, originally from Control Devices, uses capacitive switches, but this proved to be unrealiable. The replacement uses a Stackpole grid. The PCBs are generally similar and have compatible interfaces.

There is an LSI chip on the board that handles key scanning and mapping to a base character. After that, the terminal is bit-paired, clearing bits 6 & 7 for CTRL and toggling bit 6 if bit 7 is set else bit 5 for SHIFT. (See character chart here.) This chip needs -12V, but there is a voltage converter in the keyboard itself.

They keyboard is connected to the terminal by a 40-pin ribbon cable. Only half of those are connected and there are only half as many again (ten) signals, each of which is wired to the two adjacent pins.

The schematic for the terminal is page 20/75 in VT05 Engineering Drawings. The schematic for a similar keyboard is page 13/19 of LK40 Engineeering Drawings. This shows the connector pinout.

Connections

Berg	Signal	AVR
A B	STROBE	PD0
K L	CHAR BIT 5	PB4
H J	CHAR BIT 6	PB5
C D	CHAR BIT 7	PB6
W X	GND	GND
Y Z	+5V	+5V
MM NN	CHAR BIT 3	PB2
PP RR	CHAR BIT 2	PB1
SS TT	CHAR BIT 4	PB3
UU VV	CHAR BIT 1	PB0

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"LK01 Keyboard\"" -DCONTROL_STROBE_TRIGGER=TRIGGER_RISING

Consul 262.3

A late Soviet Hall Effect keyboard.

• Even the keyboards with Cyrillic and Latin legends just send Latin characters.
• The arrow keys and numpad send characters with the high bit set.

Some scanned pages of documentation are in the Wiki.

Connections

Signal	Pin	AVR
KD0	6	PB0
KD1	12	PB1
KD2	7	PB2
KD3	8	PB3
KD4	11	PB4
KD5	9	PB5
KD6	10	PB6
KD7	4	PB7
STROB	16	PD0
+5V	2	5V
⏚	1,3,5	GND

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Consol 262.3 Keyboard\"" -DCHAR_MASK=0xFF -DCHAR_INVERT

Beehive B100

The keyboard interface is described in the Beehive B100 Computer Terminal - Maintenance Manual. Schematic 9 of 16 of the terminal gives the signals on the keyboard connector, an Augat 18-pin DIP.

Connections

DIP	Signal	AVR
1,9	+5V	VCC
11,18	GND	GND
8	KB IN 1	PB0
7	KB IN 2	PB1
6	KB IN 3	PB2
5	KB IN 4	PB3
4	KB IN 5	PB4
3	KB IN 6	PB5
2	KB IN 7	PB6
15	/KEYSTROBE	PD0
14	/INTERNAL OPN	PD1
12	/BREAK EN	PD2
10	/INSERT MODE	PD3
17	/AUX EN	PD4
16	/AUX ONL	PD5
13	/RESET	PD7

• INTERNAL OPN is on in conjunction with the arrow and other navigation keys, which send the VT52 ESC code.
• BREAK is on for a set period, around 1/4 sec, no matter how long it is held down.
• The three keys above ALPHA LOCK toggle mode LEDs underneath and the next three signals, whether or not the optional window key caps, INST CHAR, AUX ENBL, AUX ONLN, are present.
• RESET is triggered by pressing CTRL, SHIFT, and CLEAR HOME together.

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Beehive B100 Keyboard\"" \
  -DDIRECT_KEYS=7 -DDIRECT_INVERT_MASK=0x5F \
  -DDIRECT_ESC_PREFIX_MASK=1 -DDIRECT_ESC_PREFIX_VT100 \
  -DDIRECT_KEY_2=DIRECT_BREAK

Amkey SNK-58

Part of some kind of (T-Bar?) EIA test equipment. The keys legends have the ASCII CTRL character name on the corresponding key.

Command Keys

These blue keys send codes with the eight it set.

Legend	Code
HEX PAIR	81
CMND	82
STEP	83
RUN	84
CLEAR	85
<-	86
STOP	87

Connections

Connects with a 20-pin ribbon cable with a key pin missing.

The side opposite the key pin has power: starting from that end, two pins of +5VDC and eight pins of ground.

The keyed side has, after the missing pin, the strobe signal (idle high), then eight data bits in order 4, 5, 6, 7, 3, 2, 1, 0.

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Amkey SNK-58 Keyboard\"" -DCHAR_MASK=0xFF

Apple II / II Plus

Earlier versions of the keyboard had an NSC MM5740 encoder chip. This was replaced by a separate encoder daughter board with an SMC KR3600. (A keyboard without the daughter card requires scanning the matrix directly through the 26-pin connector, which is a different project.)

Note that the encoders do not generate lowercase characters. In the case of MM5740, this is a restriction of the chip. The KR3600 has 10 output pins to allow for selecting alphabetic shifting. And the encoder board has two jumpers that can be cut and a toggle switch installed to go from B5 and B6 to B9 and B8 for K4 and K5 and thereby get both cases.

Some sources:

• Understanding the Apple II
• Apple II/II+ Keyboard Socket
• Early Apple Keyboards

Connections

A ribbon cable connected to a 16-pin DIP on the motherboard.

The encoder also needs -12VDC, but not with very much current, so a cheap converter from the USB +5VDC works fine.

DIP	Signal	AVR
1	+5V	VCC
2	STROBE	PD0
3	/RESET	PD1
4
5	K5	PB5
6	K4	PB4
7	K6	PB6
8	GROUND	GND
9
10	K2	PB2
11	K3	PB3
12	K0	PB0
13	K1	PB1
14
15	-12V
16

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Apple II Keyboard\"" \
  -DCONTROL_STROBE_TRIGGER=TRIGGER_RISING \
  -DDIRECT_KEYS=1 -DDIRECT_INVERT_MASK=1 -DDIRECT_DEBOUNCE=5 -DENABLE_SOF_EVENTS \
  -DDIRECT_KEY_1=DIRECT_BREAK

Apple 1

The original Apple also connected to the keyboard with a 16 pin DIP (B4) and was not manufactured with a keyboard of its own (see Operation Manual). The pinout is not the same, however. It additionally needs +12V.

DIP	Signal	AVR
1	RESET	PD1
2	B4	PB3
3	B3	PB2
4	B2	PB1
5	B1	PB0
6	B5	PB4
7	B6	PB5
8	B7	PB6
9	GROUND	PB4
10	+12V
11	-12V
12	CLEAR SCREEN	PD2
13
14	STROBE	PD0
15	B8	PB7
16	+5V	VCC

Examples:

• Early Datanetics keyboards (see notes they took from Apple).

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Apple I Keyboard\"" \
  -DCONTROL_STROBE_TRIGGER=TRIGGER_RISING \
  -DDIRECT_KEYS=2 -DDIRECT_INVERT_MASK=1 -DDIRECT_DEBOUNCE=5 -DENABLE_SOF_EVENTS \
  -DDIRECT_KEY_1=DIRECT_BREAK -DDIRECT_KEY_2=DIRECT_HERE_IS

Maxi-Switch 216004

Uses an SMC 3603 encoder, which seems to be the same as the KR3600.

Connections

Has an 18-pin edge connector.

Pin	Signal	AVR
A	K44 (BRK)	D1
B	K44 (BRK)	GND
C	K14 (HERE IS)	D2
D	K14 (HERE IS)	GND
E	REPT ENABLE
F	STROBE	D0
H	B9	*
J	B7	B6
K	B6	B5*
L	B5	B4
M	B4	B3
N	B3	B2
P	B2	B1
R	B1	B0
S	VCC	VCC
T	VDD	GND
U
V

A SPDT switch can be installed to select between encoder B9 and B6 for output B5 allows choosing between uppercase-only and upper- and lowercase.

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Maxi-Switch 216004 Keyboard\"" \
  -DCONTROL_STROBE_TRIGGER=TRIGGER_RISING \
  -DDIRECT_KEYS=2 -DDIRECT_INVERT_MASK=3 -DENABLE_SOF_EVENTS -DDIRECT_DEBOUNCE=5 \
  -DDIRECT_KEY_1=DIRECT_BREAK -DDIRECT_KEY_2=DIRECT_HERE_IS

Jameco JE610

Another keyboard sold to early hobbyists. (Datasheet). It uses the GI AY-5-2376 encoder.

Output is via a 16-pin DIP (J1) and an 18-pin edge connector (P1).

Connections

J1	P1	Signal	AVR
1	3	NEG STROBE	PD0
2	5	D5	PB5
3	7	D0	PB0
4	9	D1	PB1
5	11	D2	PB2
6	13	D3	PB3
7	15	D4	PB4
8	1718	GROUND	GND
9	16	-12V
10	14	UD1	PD1
11	12	UD2	PD2
12	10	D6	PB6
13	8	D7	PB7
14	6	PARITY
15	4	POS STROBE
16	1,2	+5V	VCC

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"JE610 Keyboard\"" \
  -DDIRECT_KEYS=2 -DENABLE_SOF_EVENTS -DDIRECT_DEBOUNCE=5 \
  -DDIRECT_KEY_1=DIRECT_ANSWERBACK_2 -DANSWERBACK_2="\"UD1\\r\\n\"" \
  -DDIRECT_KEY_2=DIRECT_ANSWERBACK_3 -DANSWERBACK_3="\"UD2\\r\\n\""

TEC EKA-9100

(Schematic). There is no program logic on this board: it is all done with 74-series TTL.

The keyboard connects via a DC-37 d-sub connector, with only 17 (15 distinct) signals.

Connections

DC	Signal	AVR
1	+5V	VCC
2	+5V	VCC
6	/KBDACK	PC7
11	DATA 1	PB0
12	DATA 2	PB1
13	DATA 3	PB2
14	DATA 4	PB3
15	DATA 5	PB4
16	DATA 6	PB5
17	DATA 7	PB6
18	/STROBE	PD0
19	/CLRSCN	PD1
26	/BELL	PC6
27	/BREAK	PD2
31	GND	GND
33	CHASSIS GND
36	GND	GND

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"TEC EKA Keyboard\"" \
  -DBELL_MODE=BELL_MODE_LOW \
  -DREADY_ACK_MODE=READY_ACK_MODE_KEY_ACK -DREADY_ACK_ON_STATE=READY_ACK_ON_LOW -DREADY_ACK_DELAY_MSEC=250 -DENABLE_SOF_EVENTS \
  -DDIRECT_KEYS=2 -DDIRECT_INVERT_MASK=3 -DDIRECT_DEBOUNCE=5 \
  -DDIRECT_KEY_1=DIRECT_HERE_IS -DDIRECT_KEY_2=DIRECT_BREAK

Scientific Devices

This keyboard has no model number, although very similar looking ones are labeled KBMO two, suggesting that this might be KBMO one. See, for instance, here and here.

Has an 24-pin edge connector, which is numbered 1-12 and 13-24 rather than A-N.

There are 7 LEDs lit directly by the data output signals. They therefore show the (LSB left, inverted) ASCII character while the key is help down.

Needs -12V for the CMOS keyboard decoder.

Connections

Pin	Signal	AVR
1	-12V	VCC
2	DATA 1	PB0
3	DATA 2	PB1
4	DATA 3	PB2
5	DATA 4	PB3
6	DATA 5	PB4
7	DATA 6	PB5
8	DATA 7	PB6
9	DIRECT 12 (R4 right, HERE IS)	PF4
10	DIRECT 13 (R3 right)	PF5
11	DIRECT 14 (R2 right)	PF6
12	DIRECT 15 (R1 right, BREAK)	PF7
13	/STROBE	PD0
14	STROBE
15	GND	GND
16	+5V	VCC
17	GND	GND
18	GND	GND
19	DIRECT 1 (R1 second right, CLEAR)	PD1
20	DIRECT 2 (R2 second right)	PD2
21	DIRECT 3 (R3 third right, RETURN)	PD3
22	DIRECT 4 (R3 second right)	PD4
23	DIRECT 5 (R4 second right)	PD5
24	DIRECT 7 (R1 left)	PD7

On this board, the trace for pin 21 has been cut and wires added so that that switch decodes from the matrix as ASCII CR.

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Scientific Devices Keyboard\"" \
  -DDIRECT_KEYS=15 -DDIRECT_INVERT_MASK=0x7FFF -DENABLE_SOF_EVENTS -DDIRECT_DEBOUNCE=5 \
  -DDIRECT_KEY_12=DIRECT_HERE_IS -DDIRECT_KEY_15=DIRECT_BREAK \
  -DDIRECT_KEY_1=DIRECT_ANSWERBACK_2 -DANSWERBACK_2="\"Goodbye\\r\\n\""

Maxi-Switch 2160094

Uses a MCS-48 controller with firmware label MS 0319019.

Connections

Has 16-pin DIP and 18-pin edge connectors.

DIP	Edge	Signal	AVR
1	A	K45	D1
2	B	K45	GND
3	C	K15	D2
4	D	K15	GND
5	E	/REPT
6	F	/STROBE	D0
7	H	B5	B5
8	J	B6	B6
9	K	B4	B4
10	L	B3	B3
11	M	B2	B2
12	N	B1	B1
13	P	B0	B0
14	R	VCC	VCC
15	S	GND	GND
16		N/C
	T	JUMPER
	U	JUMPER
	V	JUMPER

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Maxi-Switch 2160094 Keyboard\"" -DCHAR_INVERT

Xerox 820 ASCII

The X928 ASCII only Maxi-Switch variant of the 820 keyboard pictured here.

Connections

Has a DB-25 connector.

J2	Signal	AVR
1	DB0	B0
2	DB1	B1
3	DB2	B2
4	DB3	B3
5	DB4	B4
6	DB5	B5
7	DB6	B6
8	DB7	B7
9	/STROBE	D0
10-12	N/C
13	+5V	+5V
14-22	GND	GND
23,24	N/C
25	GND	GND

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Xerox 820 ASCII Keyboard\""

Datamedia 1520

The PCB this was tested on is 3DAAA022, but similar ones should be the same.

Connection to the keyboard is through a DB-25 to a 30-pin edge connector.

The schematic for variants of this keyboard start on page 40 in Datamedia Elite 1520A Technical Manual.

Connections

Needed for this:

| DB-25 | Edge | Signal | AVR | | 21 | 1 | GND | GND | | 23 | 2 | +5V | +5V | | 22 | 3 | /RPT | PD1 | | 2 | 4 | /KBDTAPE | PD2 | | 4 | 5 | | | | 6 | 6 | | | | 18 | 13 | /BRK | PD3 | | | 15 | /STRBDIS | | | 14 | A | GND | GND | | 16 | B | +5V | +5V | | 1 | C | /KB1 | PB0 | | 3 | D | /KB2 | PB1 | | 5 | E | /KB3 | PB2 | | 7 | F | /KB4 | PB3 | | 9 | H | /KB5 | PB4 | | 11 | J | /KB6 | PB5 | | 13 | K | /KB7 | PB6 | | 20 | L | /KBSTR | D0 | | | M | /KBSTR | | | 10 | P | -12V | | | 8 | R | | PD4 | | 12 | S | | |

-12V is only needed if the chip in slot 12 is present, which it was not in the one tested.

There is a jumper FF to connect switch 78 (LOAD TAPE) to GG switch 13 (TAPE), making them both (4), or alternatively EE to (R). The default seems to be FF-GG, so both keys are the same.

Build

PARALLEL_KBD_OPTS = -DKEYBOARD="\"Datamedia 1520\"" \
  -DCHAR_INVERT \
  -DDIRECT_KEYS=3 -DDIRECT_INVERT_MASK=7 -DENABLE_SOF_EVENTS -DDIRECT_DEBOUNCE=5 \
  -DDIRECT_KEY_3=DIRECT_BREAK