HDS Concept AVT-APL+ Keyboard

00-readme.md

HDS Concept AVT-APL+ Keyboard

A Keytronics foam and foil keyboard for an APL capable terminal from 1984.

Protocol

The keyboard just sends idle low, 9600 baud ASCII, with special codes for function keys. It is therefore rather impractical to have it implement a USB keyboard.

Communication in the other direction turns on the LEDs (L1, L2, L3, L4, CAPS LOCK) with a bit mask with odd parity.

Connections

The cable from the keyboard has a DIN-5 connector.

DIN	J2	Color	Signal
1	1	Red	GND
2	2	Brown	RXD (from kbd)
3	4	Orange	+5V
4	5	Yellow	GND
5	6	Gray	TXD (to kbd)

ascii.md

ASCII codes

Printing characters match the regular and shifted ASCII codes from the corresponding non-APL keyboard.

Function keys have the eighth bit set.

Legends	Code	Shift
RESET BREAK	C3	C4
PRINT SCRN	C8	C9
CMD	C1	C2
PRINT	C6	C7
F1 INSERT	A0	B0
F2 DEL CHAR	A1	B1
F3 DEL INS L	A2	B2
F4 ERASE	A3	B3
F5 SEND	A4	B4
F6	A5	B5
F7	A6	B6
F8	A7	B7
F9	A8	B8
F10	A9	B9
F11	AA	BA
F12	AB	BB
PAGE	CA	CB
HOME SAVE	C5
UP NEXT LINE	CC	CC
SETUP	C0	C0
SCROL	CD	CE
LEFT ←	CF	CF
DOWN NEXT VALUE	D0	D0
RIGHT →	D1	D1
HALT ESCAPE	F9	FA
1 ¨ !	31	21
2 ¯ @	32	40
3 < #	33	23
4 ≤ $	34	24
5 = %	35	25
6 ≥ ^	36	5E
7 ≠ &	37	26
8 ≠ *	38	2A
9 ∨ (	39	28
0 ∧ )	30	29
+ - =	2D	5F
× ÷ + =	3D	2B
◊ $ ~ `	60	7E
BACK SPACE	F6	F7
BTAB TAB	F8	D4
Q ?	71	51
W ⍵	77	57
E ∈	65	45
R ⍴	72	52
T ∼	74	54
Y ↑	79	59
U ↓	75	55
I ⍳	69	49
O ○	6F	4F
P ⋆	70	50
← →	5B	5D
⊢ ⊣	5C	7C
LINE FEED	F2	F3
DEL	F4	F5
CAPS LOCK	D6	D6
A ⍺	61	41
S ⌈	73	53
D ⌊	64	44
F _	66	46
G ∇	67	47
H ∆	68	48
J ∘	6A	4A
K '	6B	4B
L ⎕	6C	4C
[ ( ; :	3B	3A
] ) ' "	27	22
{ }	7B	7D
RETURN	F0	F1
STAT	D2	D3
Z ⊂	7A	5A
X ⊃	78	58
C ∩	63	43
V ∪	76	56
B ⊥	62	42
N ⊤	6E	4E
M '	6D	4D
, ; <	2C	3C
. : >	2E	3E
/ \ ?	2F	3F
SPACE	20	20
F13 PF1	81	BC
F14 PF2	82	BD
F15 PF3	83	BE
F16 PF4	84	BF
7	91	91
8	92	92
9	93	93
-	88	88
4	8E	8E
5	8F	8F
6	90	90
,	86	86
1	8B	8B
2	8C	8C
3	8D	8D
ENTER	85	85
0	8A	8A
.	89	89

hds.ino

#include <util/parity.h>

void setup() {

  Serial.begin(115200);
  while (!Serial) {
  }

  Serial1.begin(9600, SERIAL_8N1_RXINV_TXINV);

  pinMode(13, OUTPUT);
}

void loop() {
  if (Serial1.available()) {
    uint8_t ch = Serial1.read();
    Serial.println(ch, HEX);
  }

  static uint32_t last_time = millis();
  uint32_t now = millis();
  if (now - last_time > 1000) {
    static uint8_t n = 0;
    uint8_t ch = n | (parity_even_bit(n) ? 0x00 : 0x20);
    Serial1.write(ch);
    n = (n + 1) & 0x1F;
    last_time = now;
  }
}