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Part 3.
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Yep, it's me again... :)
Well from Parts 1 & 2 we accessed the simplest of the hardware registers
that have some use for specific applications. The Audio Filter and the
Video Mode swtiches.
We are now going start messing with the AMIGAs Games/Joystick Port.
This is a VERY capable port and has many, MANY uses other than the
known standard ones. When using pure assembler/machine-code it can be
accessed at 75+KHz when using a standard A1200(HD) or 25+KHz on the
A500, A500+ and A600(HD). Big box AMIGAs can access it even faster.
This makes the games port very useful indeed.
The first access we are going to use is the ports' FIRE button.
This is a TTL, (Transistor Transistor Logic), level digital input/output
pin. It defaults as a digital input upon any RESET of the computer.
From now on I will describe some simple project that can be connected
to this port that is NOT pertaining to normal Joystick use.
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Pin 6, The FIRE Button.
-----------------------
Pin 6 of the 9 pin ~D~ type games plug at the rear of the A1200(HD) is the
FIRE button. It can be programmed as either INPUT, (normal bootup mode),
OR OUTPUT via two registers. These registers are:-
1) CIAAPRA - pra, 0xBFE001, 12574721 - bit 7; the FIRE button.
2) CIAADDRA - ddra, 0xBFE201, 12575233 - bit 7; 1 = OUTPUT, 0 = INPUT.
This button has been used by myself as a 10MHz Frequency Counter using
pin 6 in standard INPUT mode. If the AMIGA is booted up then CIAADDRA
does NOT need to be altered - so for the first part I will describe
a simple project using pin 6 in this mode.
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A Simple Logic Probe.
---------------------
Logic probes are used to detect logic states of 0 or 1 in various parts
of a digital circuit board. The games port pin 6 can be used as a very
limited logic probe. It will only work with basic logic states and at
very low frequencies BUT is useful nevertheless. The hardware is SO
simple it meets my CRITERIA with ease.
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Technical Specifications:-
--------------------------
Maximum Input Voltage....... + or - 12 Volts maximum.
Over Voltage Protection..... Yes, limited to 10 Seconds duration.
Input Impedance............. Greater than 1.5 KilOhms.
Detectable Pulse Width...... 0.5 second approximately.
Indeterminate DC Range...... N/A.
TTL Logic 0................. 0 Volts to 1.0 Volts, + or - 0.25 Volts.
TTL Logic 1................. 1.25 Volts to 4.75 Volts, + or - 0.25 Volts.
Display..................... Standard Workbench window.
Negative Logic Detection.... No.
Settling Time............... Approximately 1 second for a standard
A500 and OS1.3x.
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Circuit Diagram:-
-----------------
The INPUT 1.5 KilOhm resistor is a current limiter and at the tapping
point, pin 6, two small signal silicon diodes are placed ~polarity
reversed~ across the supply as shown in the circuit below.
(Note, best viewed in ~topaz 8 font~.)
Pin 7. *-------------------+ <-- +5V.
|
|
--+-- +
/ \ D1, (D4), (1N4148).
'---`
|
| R1, (R2).
Pin 6, (9). *--------------*-*-------\/\/\/-------O Probe INPUT.
| (1.5 KilOhms). Blue, (White).
|
--+-- +
/ \ D2, (D3), (1N4148).
'---`
|
|
Pin 8. *---------------------*--------------*-----O GND.
| (Screen/Black).
^ __|__
| /////
|
+-- 9 Way ~D~ Type socket pin numbers.
If there is a voltage swing greater than APPROXIMATELY +5.6V or less
than -0.6V then this voltage is current limited through R1 and CLAMPED
to either the +5V rail or GND. Although the photographs and drawings
show a white wire connected to another 1.5 KilOhm resistor and linked
to pin 9, then this can be ignored until a future magazine issue where
it WILL be required. As it is SO simple you may as well build it now
ready for that future project/experiment, including the white wire... :)
Parts List:-
------------
(Special part numbers from MAPLIN for the UK, at the time of writing.)
http://www.maplin.co.uk
1) R1, (R2)...................... 1.5 KilOhms, 1/8W, resistor.
2) D1, D2, (D3, D4).............. 1N4148, silicon diode.
3) Connecting Wire............... Any, Blue, White and Black.
4) 9 Way ~D~ Type Socket......... RK61R.
5) ~D~ Shell..................... FP27E, IF you can get it to fit... :)
6) Sleeving...................... IF required.
7) Crocodile Clip Black.......... FK34M, for the other end of the cable.
8) Probe Red..................... L26BH. for the other end of the cable.
9) Small Stripboard/Veroboard.... 10 holes by 4 tracks in size.
All components should be available from ANY source.
All tolerances + or - 10% or better.
Refer to photographs and drawings for the construction method.
(The drawings DO NOT show the fitting of the crocodile clip and the probe,
it is assumed that by now it will be obvious where these go at the other
end of the two wires; the blue wire connected to the probe, the black wire
connected to the crocodile clip.)
Standard tools and soldering equipment as required.
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AmigaBASIC Code:-
-----------------
10 REM Simple games port pin 6 READ access, Games Port Logic Probe.
20 REM Public Domain, original copyright, (C)2006, B.Walker, G0LCU.
30 REM Written for - http://www.thecryptmag.com - as a simple project.
40 REM This project is for ALL ages.
50 REM See the drawing for the circuit.
100 REM Set up a simple window.
110 WINDOW 1,"Games Port Logic Probe.",(0,0)-(462,64),6
120 CLS
130 REM Set up any variables.
140 LET a$="(C)2006, B.Walker, G0LCU."
150 LET version$=" $VER: Logic-Probe.B_Version_0.80.00_(C)29-09-2006_G0LCU."
150 LET state=1
190 REM Set up the display.
200 PRINT
210 PRINT version$
220 PRINT
230 PRINT " Press the SPACE BAR or Esc keys to Quit."
240 LOCATE 7,23
250 PRINT "Logic state";state;CHR$(8);". "
390 REM This is the main loop.
400 LET a$=INKEY$
410 IF a$=" " OR a$=CHR$(27) THEN GOTO 1000
420 LET state=PEEK(12574721&)
430 IF state>=128 THEN LET state=1
440 IF state=1 THEN GOTO 460
450 IF state<=127 THEN LET state=0
460 LOCATE 7,23
470 PRINT "Logic state";state;CHR$(8);". "
500 GOTO 400
990 REM Safe exit from the program.
1000 WINDOW CLOSE 1
1010 SYSTEM
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ARexx Code:-
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/* Logic Probe using the ARexx interpreter. */
/* ---------------------------------------- */
/* LP.rexx, (C)01-10-2006, B.Walker, G0LCU. */
/* ---------------------------------------- */
/* Released as Public Domain Software. */
/* ---------------------------------------- */
/* Set up any constants or variables. */
state=1
logic='1'
copyright='9'x'$VER: Logic-Probe.rexx_Version_0.80.00_01-10-2006_(C)G0LCU.'
/* Use ECHO for ordinary printing to the screen and SAY for printing results. */
/* Set up the games port logic probe screen. */
ECHO 'c'x
ECHO 'd'x'9'x'9'x'9'x'Click left mouse button to Quit.'
ECHO 'a'x'9'x'9'x' Logic Probe using pin 6 of the games port.'
ECHO 'a'x'a'x'9'x'9'x'9'x' Logic state = 1.'
/* This is the main loop. */
DO FOREVER
/* Read the 'pra' register for bit 7, pin 6 of the games port. */
/* ALSO bit 6, pin 6 of the mouse port from the same register... :) */
state=IMPORT('00BFE001'x,1)
IF BITTST(state,7)=1 THEN logic='1'
IF BITTST(state,7)=0 THEN logic='0'
/* Left mouse button to quit the program. */
IF BITTST(state,6)=0 THEN CALL getout
/* Print the results to the screen. */
SAY 'b'x'9'x'9'x'9'x' Logic state = '||logic
END
/* Exit the program safely. */
getout:
EXPORT('00BFE001'x,'FC'x,1)
ECHO 'c'x
SAY copyright
EXIT(0)
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CIA == Complex Interface Adaptor.
TTL == Transistor Transistor Logic.
CIAADDRA == CIA 'a' 'ddra', CIA 'a' data direction register 'a'.
CIAAPRA == CIA 'a' 'pra', CIA 'a' programmable register 'a'.
The code sections above ignore the CIAADDRA, 'ddra' register as this is
correctly set during a boot or reboot. The 'ddra' is the 'data direction
register a' for the CIAA 'pra'. As we are READING CIAAPRA register AT bit 7,
(and bit 6 because bit 6 is the left mouse button), then there is no reason
to switch the 'ddra' register to READ mode for these two bits of the
register CIAAPRA, hence no line in either code segment to change the state
of this register. CIAADDRA is set to 3 decimal and as a '1 = output' then
bits 0 and 1 of CIAAPRA CAN be written to. See below for bit 0, and bit 1
is the audio filter control bit. See the last magazine issue about writing
to bit 1.
Now 'pra' is the 'programmable register a' for CIA 'a' and all we need to
do is read bit 7 as this equates to pin 6 of the games port, pin 6 of the
mouse port equates to bit 6 of 'pra' but we are not going to pursue this
any further as the mouse is always in use for other functions and for all
intents and purposes is 'out of bounds'.
If the decimal value of 'pra' is greater than OR equal to 128 then bit 7
must be at TTL level high so therefore bit 7 MUST equal a logic 1. If the
decimal value is less than OR equal to 127 then bit 7 must be at TTL level
low so therefore bit 7 MUST equal a logic 0.
Bit 0 of CIAA 'pra' MUST NEVER be altered from its value as this is 'in
theory' connected to the physical RESET line. Instability could/would result
if you mess about with this bit. SO BEWARE!!!.......
DO NOT ALTER THIS BIT, (BIT 0), UNLESS YOU KNOW WHAT YOU ARE DOING...
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Just a quick note that ALL of my components for this project were RECYCLED
from the 'junk' box and NOTHING was purchased NEW AT ALL, so for me all it
cost was my time... :)
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IMPORTANT:-
-----------
The Legal Stuff:-
-----------------
These programs are Freeware and no profit will be made from them,
also all of the files must remain unaltered and intact including this
one. The author is not responsible for any damage to, or loss of, or
failure of equipment or data caused in any way by the use of these
programs. There is NO warranty with the use of these software releases
and YOU USE THEM AT YOUR OWN RISK.
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Testing Evaluation:-
--------------------
An A1200(HD) in 2MB, 6MB and 10MB modes using trapdoor memory AND/OR
PCMCIA memory expansions. Also tested on an A600(HD) in 2MB and 6MB
modes. All test conditions were/are running STANDARD KS2.0x to 3.1x,
and using standard ~topaz 8~ fonts throughout.
I have no idea what a strange configuration setup will create so refer
to the ~The Legal Stuff~ above.
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WARNING.
--------
1) DISCONNECT any faulty equipment under test from the MAINS supply.
2) If a DC supply is used do NOT reverse polarity the connections.
3) Do NOT power up any electronic item until it is safe to do so.
4) CHECK and RECHECK all of your construction and repair work thoroughly.
5) Handle ALL tools used with care.
6) Beware of ALL types of solvents, glues and etching fluids.
7) NEVER leave a soldering iron switched on unattended.
8) KEEP everything OUT of the reach of small children.
9) Switch OFF the AMIGA before disconnecting or connecting any hardware.
10) And finally read 1) to 9) again.
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Contact:-
---------
Mr Barry Walker, G0LCU.
Email:- wisecracker@tesco.net
URL:- http://homepages.tesco.net/wisecracker/G0LCU.HTM
Author of the ~TestGear?~ projects in the ~docs/hard~ drawer of AMINET.
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A very useful HardWare related site, (C) Anthony Hoffman, for
modifications, schematics, repairs and the like is:-
http://amiga.serveftp.net/
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That's all for now folks... :)
| © RIYAN Productions |
