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1992-08-20
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334 lines
IBM Keyboard Interfact Project, by Eric Rudolph, 1991.
No Copyright Whatsoever, but I would like credit where it's due.
This is documentation for the circuit I built which converts the information
put out by an XT or AT keyboard to that which can be recognized by an Amiga.
The circuit itself is a simple 8051 with an address latch and an Eprom.
It is inserted between the keyboard and the Amiga and sends data in both
directions to the Keyboard and the Amiga.
Parts count could be reduced by using an 8751 which contains a 4k internal
Eprom. Seeing as how I don't know how to program them yet, I will stick to
the above design, but I am sure it's not hard to do. :-\
Full Parts List:
================
1) Intel 8031/8051, preferrably low power
2) 74373 address latch
3) 2732 Eprom
4) 11.059 MHZ crystal
5) 2 30pf caps
6) 1 10k resistor, 1/4 watt
7) 1 10uF electolytic cap
8) 2 momentary pushbutton switches. Neither is really needed.
10) connectors to the Amiga and the IBM
The total cost for these parts come to about $18.00 minus box and breadboard.
It certainly would be cheaper to use some used components.
Wiring List:
============
INTEL 8031/8051:
Port1, pins 1-8 can be connected in any manner whatsoever,
so long as you change the source code. You can relocate
the lines to the Keyboard and the Amiga wherever suitable.
If you understand the 8051 or read the 8051 manual, it will make more
sense.
pin to
=== ==
1(p1.0) Keyboard Clock. Female 5-pin, pin #1
2 Keyboard Data, Female 5-pin, pin #2
3
4 Amiga Clock
5 Amiga Data
6 Amiga Reset
7
8(p1.7) XT/AT pin. Tie low to always convert an XT keyboard.
For Auto detect, leave pin unconnected.
9(reset) to - side of 10uF cap & 10k resistor & pushbutton switch
only if you want a manual CIRCUIT reset switch.
10(p3.0)
11
12(int0) pushbutton switch2
13-16
17(p3.7)
18 clock crystal & 30pf cap1
19 clock crystal(other pin) & 30pf cap2
20 Ground
21(a8) Eprom Addr8, 2732 pin#23
22 Eprom Addr9, 2732 pin#22
23 Eprom Addr10, 2732 pin#19
24(a11) Eprom Addr11, 2732 pin#21
25-28
29 Eprom Read, 2732 pin#20
30 373 Gate, pin# 11
31 Ground
32(ad7) 373 D7, pin#13 & Eprom Data7, pin#17
33 373 D6, pin#14 & Eprom Data6, pin#16
34 373 D5, pin#8 & Eprom Data5, pin#15
35 373 D4, pin#7 & Eprom Data4, pin#14
36 373 D3, pin#4 & Eprom Data3, pin#13
37 373 D2, pin#3 & Eprom Data2, pin#11
38 373 D1, pin#17 & Eprom Data1, pin#10
39(ad0) 373 D0, pin#18 & Eprom Data0, pin#9
40 +5 Volts
74373:
1 Ground
2 Eprom Addr2, pin#6
3 done
4 done
5 Eprom Addr3, pin#5
6 Eprom Addr4, pin#4
7 done
8 done
9 Eprom Addr5, pin#3
10 Ground
11 done
12 Eprom Addr7, pin#1
13 done
14 done
15 Eprom Addr6, pin#2
16 Eprom Addr1, pin#7
17 done
18 done
19 Eprom Addr0, pin#8
20 +5 volts
2732 Prom:
1-11 done
12 Ground
13-17 done
18 Ground (chip enable. Doesn't save power very much)
19-23 done
24 +5 volts
crystal:
connected between 8051 pins 18 and 19
30pf cap1:
connected between a lead of cystal and ground
30pf cap2:
connected between other lead of crystal and ground
10uF Electrolytic Cap:
minus end to 8051 pin9, + end to +5 volts.
10k resistor:
tied between ground and 8051 pin 9
VVV reset pushbutton switch. This is not absolutely necessary.
Pushbutton Switch1:
tied between 8051 pin9 and +5 volts
VVV only use if you want a one-button hard reset.
Pushbutton Switch2: (amiga reset switch)
tied between 8051 pin12 (int0) and ground
5-pin Female IBM connector:
Connect plus voltage pin to +5 volts
Connect ground pin to ground
connect clock and data as in above
(pin1=clock, pin2=data, pin3=NC, pin4=ground, pin5=+5v)
(as you face the back of the 5-pin female din, with the notch pointing up,
the pin order from left to right is 1,4,2,5,3)
Amiga Connector: each of the amiga connectors for the 500/1000/2000 will
be different.
On the Amiga 1000, the keyboard connects by means of a telephone
HANDSET connector with a regular phone handset cord. The pins
from left to right on the back of the Amiga 1000 are +5,clock,data,GND.
If you make this circuit yourself, I suggest purchasing a little jack
from the local telephone repairman. They are fairly standard jacks
I believe. Connect red on the jack to +5,white to clock,greeen to
data, black to ground. (On the circuit board, that is...)
Clock and Data are wherever you locate them in the source code.
As it stands, Amiga Clock is on pin 3 of the 8051, and Data is
on pin 4.
For the Amiga 500, there is a 8 pin straight line on the mother board.
These pins from left to right are
1. Data
2. Clock
3. Reset
4.+5
5 Not connected. (Key)
6.Ground
7. Status (not used)
8. Disk Light (not used)
Make yourself a special adaptor that connects your amiga to the circuit.
You WILL need to connect the reset line if you want to soft reset from
the keyboard. The A500 only resets by having the Reset line driven low.
It says in my hardware manual here that The connector TO the keyboard
goes as follows:
1: Clock
2: Data
3: Not connected.
4: Ground
5: +5 volts.
I imagine it's just like the AT connector, but it's a shame they don't use
the same data signals!
VERY IMPORTANT:!!!! The cord from the Amiga to the Converter must be
very very short and have very low resistance for this circuit to run on it's
own power. Do NOT use a long handset cord, it will load down the power lines.
IT's made of ribbon copper wound around some white stuff and it conducts poorly
on purpose. I used a hackup phone handset cord that is only about 3 inches
long. That works fine. You may need to get a phone repairman to make the
little cord special. He can do it, I know. It's a common thing. It shouldn't
be expensive. The one he made for me cost 1$.
That's it!
====================================================================
A little background on the IBM AT keyboard:
The keyboard I used for this circuit was a BTC 5339sx. It costs about $40
Lucky Computers, 1-800-348-5825. I have also tested the circuit on a
standard PC keyboard, and an HP Vectra AT keyboard.
The AT keyboard DIN connector has 5 pins. Pin 3 is called Reset, but it's
reserved, so we can't use it. Forget it exists on the AT keyboard. They just
charge you money for it. (joke) Open collectors drive the clock and data pins,
so when they are not driven low, they float at 5 volts.
The keyboard transmits data by bits, each synchonous somehow with the clock
line. They keyboard when clocking in or out data, always runs the clock.
The controller can drive the clock line, but not with reference to data.
When the Keyboard sends data, it first sets the data, then drives
clock low, then high, and then changes the data to the next value.
The AT uses 11 bits for a transmission, 1 start bit (0), 8 data
bits, 1 parity bit-set if the number of 1's in the data bits is even, and
a stop bit (1). When the keyboard sends it's last bit, the stop bit, the
controller must drive clock line low as a handshake and to tell the
keyboard not to send until clock goes high again.
Theoretically, the controller could interrupt the sending of the
bits, but I consider this unnecessary, and don't bother with it.
When the computer needs to send a command to the keyboard, it sets clock
line high and the data line low. When the keyboard sees this, it will
start clocking pulsed on the data line.
Then, the controller must look for the clock line going low, set the data
bit, wait for the clock to go high, then wait for the clock to go low
again, and then change the bit. Thus, it changes the data in the middle
of the clock low pulse. When the keyboard has received it's 10th bit,
it will drive the data line low while at the same time clocking out
an extra clock low pulse. Then, it expects a handshake of the clock line
low from the controller.
0 1 2 | 7 P stop extra
Clock:------------\___/---\___/---\___/---\___/---\___/---\___/---\___/end
Data:-------\_______00000001111111122222|6677777777PPPPPPPP1111xxxxxxxx_____
Notice there is NO start bit when the controller sends data to the Keyboard.
Special Commands the Keyboard can Send to the Controller:
-----------------------------------------------------------
00 Keyboard buffer overflowed
AA Selftest passed
FA The command sent was received correctly
FE The command sent was received poorly. Please resend.
Special Commands the Controller can Send to the Keyboard:
-----------------------------------------------------------
ED Set the LEDs according to next byte I send
bit 0=Scroll lock 1=on
bit 1=Num lock
bit 2=Caps lock
bits 3-7 must be 0
F4 clear the key buffer and start scanning
F6 restore default values
FE retransmit last character, please
FF Reset, you stupid keyboard!
Whew! That about raps it up for the AT keybard! Enough said, right?
XT keyboards transmit much the same way except they only use 10 bits.
Two start bits (both high) and 8 data bits, transmitted in order 0-1-2...-7
The last bit is a make/break bit which is 1 to signify a break.
The XT can have no commands sent to it. The way to reset it is to drive
the Clock line low for some longish period of time. The keyboard will not
send data (it will hold off) if the data line is being held low by an
external source (the controller)
AMIGA SIDE=========================================
Now I bet you are all wondering which keys are mapped to which keys.
I am using the 101 AT keyboard.
AT Amiga
== =====
Left Ctrl Left Amiga
Right Ctrl Right Amiga
F11 Numeric Keypad (
F12 Numeric Keypad ) (doesn't work on A1000's)
Capslock Control (IF used in conjunction with another key)
Delete Delete
Page Down Help
PrintScreen Left Amiga
ScrollLock Right Amiga
NumLock Control
(the above three keys mapped for easy one-hand reset)
Insert Amiga+Left Cursor
Home Amiga+Up Cursor
End Amiga+Down Cursor
PageUp Amiga+Right Cursor
(the above keys mapped for easy mouse pointer control in workbench.)
The BTC keyboard I used also included a Macro key (conveniently) that
is mapped as a control key.
All other keys are mapped exactly the same.
Since the Control Keys on the AT are mapped to the Amiga keys,
I made a little routine that defines the Capslock Key to work as
Control if you hold it down first, then type the other key.
Just use it as you would an ordinary Control key.
This only works for the AT, not the XT since I can't control the lights
on the XT.
The explanation for how the Amiga Keyboard works is provided in the
Hardware Reference Manual. I will not repeat this info here, for fear of
copyright infringements and because the manual is cheap and a valuable
must for anyone who indulges in this kind of thing.
<><><><><><><><><><><><><><><><><><><><><><><><><><><><>
SOFTWARE:
I have included the source and the machine code for the software that
runs this circuit. The timing loops are pretty stringent so if you want to
change things, better have a logic analyzer on hand!
I am also going to include a simple 8051 code assembler for those who don't
like to hand-code. If you keep your programs neatly written, it should
assemble fine.
Documentation is within the program listing. It's not too hard to follow if
you know what you are doing.
Feel free to change anything you want, but before you redistribute it,
please tell me of the changes. Make it known within the program that you
have made changes.
The circuit, once built, should never have to be removed once plugged into
your computer. It should Auto Detect which style keyboard is hooked up
if the XT/AT pin (now coded as Port 1.7 (pin 8)) is not tied low.
IF for some reason the circuit does not start up fine, you may need
a reset CIRCUIT switch. This is different than the reset Computer
switch. This switch SHOULD restart the circuit and make it sync
up to the computer and the keyboard.
I will sell anybody any number of the parts needed, from circuit board
to telephone connectors to the whole thing.
Circuit board alone: 5$
Telephone connector: 1.50$
Whole thing minus case:25$ plus shipping.
Full documentation: 1$ plus postage.
Any questions? Be glad to answer em!
Phone # 503-745-5794 (Oregon)
