Floppyshop 2/Floppyshop - 2.zip/Floppyshop - 2.iso/diskmags/3565-4.665/dmg-3609/news.txt/project4.asc

Text File | 1989-04-05 | 17KB | 404 lines

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                        #                        #
                        #    DIGITAL JUNCTION    #
                        #    ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯    #
                        #     INTERFACING 4      #
                        #     ¯¯¯¯¯¯¯¯¯¯¯¯¯      #
                        #                        #
                        #     by Dave Price      #
                        #                        #
                        ##########################


     Over the past few instalment of Interfacing I have discussed  various
possibilities  that would enable the transfer of data between the  ST  and
outside world.

       We are now going to put this knowledge to use by carrying out  some
practical interfacing experiments.  Whilst I shall be basing the  software
and  hardware around the use of the cartridge and printer ports  there  is
no  reason  why the experiments cannot be carried out on  other  types  of
interface  units  such  as  the Maplin RS232 to  8-bit  I/O  port  as  the
principles  are the same although the software may well need  altering  to
suit.

     Before  starting  I  must draw your attention to  an  amendment  that
needs  to be made to the suggested printer port module (see  STEN  12).  I
had missed out a component in my circuit diagram.  The diagram should have
shown  a  transistor  on  the  strobe  line.  It  is  important  that  the
transistor  is installed as it provides buffering to the strobe  line  and
protects   the   sound   chip   from   possible   damage.    See   picture
file..USEPORT2.PC3 (<SCREENS> folder).

     The  first  project  will  prove to be a useful  little  tool  as  it
provides a visual display of what is going on at the output port and  thus
can  be very helpful for checking that the port or software is doing  what
is intended.

     PROJECT No.1 - Output Display Unit
     ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
     Basic parts list

     1 piece of stripboard 10 strips wide x 15 holes long
     8 Red LED (rectangular makes neat job but 3mm dia. will do
     1 180R 9-pin SIL resistor array (9 pins- 8 resistors 1 common)
     1 ULN2803A Octal Darlington Driver TTL **SEE NOTE BELOW
     1 18-pin DIL socket
     length of 10-way ribbon cable or other flexible insulated wire

NOTE:  Above  parts  are for an 8-bit wide port.  If  you  require  16-bit
double up on components and double width of stripboard.

       ULN2803A not absolutly necessary if using buffered output.
       ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
     See picture file..PROJECT1.PC3..(<SCREENS> folder) for layout.

     Having  built  the circuit check for  component  orientation,  solder
bridges and cuts in stripboard have been made in the correct  places.  Now
connect  the project to your interface unit making sure  connecting  wires
are in the correct order or if using plugs that they are wired correctly.
NOTE:  If you are connecting the project directly to the printer port  you
will need a 25-way 'D' type plug.  In either case do not forget to connect
your 5 volt D.C. supply.

**WARNING**  -  Any  peripherals including interfacing  projects  must  be
connected before powering up your ST.

     Upon  switching on your ST you may notice that the LEDs flash on  and
off once.  This is OK it is only the system setting its self. There may be
occasion  when  one or two LEDS may stay on,  again,  don't  worry  it  is
possible  that a spurious pulse may have caused a line to latch  on.  This
can  be cleared by sending a zero to the port as follows:-Listings in  GFA
BASIC V3.6


RESETTING PRINTER PORT - Using hardware as discussed in Interface 3
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~XBIOS(30,$20)   !Switch userport to write mode (See note below)
~XBIOS(28,0,$81) !Send zero to port

NOTE:  ~XBIOS(30,$20)  not  needed  if project is  directly  connected  to
printer  port.  See  Interface  3  (STEN  12)  for  explanation  of  XBIOS
routines.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

RESETTING CARTRIDGE PORT - Using hardware as discussed in Interface 3
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DEFFN portout(d%) = PEEK(&HFA0000+d%) !ROM4 select + output data in d%
~@portout(0)                          !Send zero to port

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

     All  LEDs should now be off indicating that all output lines  are  at
logic low (0 Volts).

This  next  program is just a little test to check each data line  (D0  to
D7) is operating correctly.

(a) Printer Port

CLS
~XBIOS(30,$20)  !Set userport hardware to output mode
DO
LOCATE 10,5
PRINT" THIS ALLOWS YOU TO SET ONE OF THE OUTPUT"
PRINT TAB(9);"LINES(D0 - D7) ON THE PRINTER PORT"
PRINT TAB(9);"ENTER -1 TO SWITCH OFF ALL LINES"
PRINT TAB(9);"PRESS RETURN TO EXIT"
LOCATE 10,12
INPUT"ENTER OUTPUT LINE (0 -7) TO SET ";a$
EXIT IF a$=""
n|=VAL(a$)
x|=2^n|
~XBIOS(28,x|,$8F)  !Output data in x|
Loop
~XBIOS(28,0,$8F)   !Reset output (all LEDs off)
END

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(b) Cartridge port

DEFFN portout(d%)=PEEK(&HFA0000+d%)
CLS
DO
LOCATE 10,5
PRINT" THIS ALLOWS YOU TO SET ONE OF THE OUTPUT"
PRINT TAB(9);"LINES(D0 - D15) ON THE CARTRIDGE PORT"
PRINT TAB(9);"ENTER -1 TO SWITCH OFF ALL LINES"
PRINT TAB(9);"PRESS RETURN TO EXIT"
LOCATE 10,12
INPUT"ENTER OUTPUT LINE (0 - 15) TO SET ";a$
EXIT IF a$=""
n%=VAL(a$)
x%=2^n%
~@portout(x%)  !Output data in x%
LOOP
~@portout(0)   !Reset output (all LEDs off)
END

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

     If  you  have wired the LED module correctly,  the number  you  enter
into the program should turn the corresponding LED on indicating that  the
line has been set to logic high (+5 volts) i.e.  entering 3 will set  data
line  D3  and therefore the corresponding LED will be  on.  You  may  have
noticed  the terms SET and RESET being used when discussing digital  logic
levels.  Generally, a digital line is SET when at logic high (1) and RESET
when at logic low (0).


     Now try the the following program:-
Printer Port

CLS
~XBIOS(30,$20)
FOR x|=0 TO 255
PRINT x|; HEX$(x|)
~XBIOS(28,x|,$8F)
DELAY 5
NEXT x|
PRINT"Press any key to exit"
~INP(2)
~XBIOS(28,0,$8F)
END

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Cartridge Port

DEFFN portout(d%)=PEEK(&HFA0000+d%)
CLS
FOR x%=0 TO 65535
PRINT x%; HEX$(x%)
~@portout(x%)
DELAY 5      ! wait for 5 seconds
NEXT x%
PRINT"Press any key to exit"
~INP(2)
~@portout(0)
END

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

     Running  this program will cause a list of decimal numbers from 0  to
255   (65535  if  using  16-bit  on  cartridge  port)  along  with   their
hexidecimal  equivalents  00  to FF (FFFF if 16-bit) to  be  displayed  on
screen.  At the same time the LEDs will display the binary equivalents  as
the  numbers  increase.  The  program has a 5 second  delay  between  each
number  which  should be ample time to note the number  displayed  on  the
screen  and the LED pattern.  To change the delay time just alter  program
line DELAY 5.

     The following program is a little more exciting.  It "walks" a  light
along the row of LEDs in the same fashion used by many advertising signs.

NOTE:  To save repetition I shall, from now on, only be providing listings
for  use  with  the suggested printer port  interface.  Anyone  using  the
cartridge  port should not have any difficulty in converting the  programs
to  suit.  The  previous  programs should serve as a  guide.  If  any  new
routines  not  mentioned  before do arise then I  shall  indicate  in  the
printer  port listings where any alterations may need to be  carried  out.
However, If anyone has problems then let me know.

Running light program

PRINT "Press mouse button to exit"
REPEAT
x=1
REPEAT
~XBIOS(28,x|,$8F)
PAUSE 5  x=x*2
UNTIL x=256
UNTIL MOUSEK
END

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

     These  small programs should give a reasonable indication as  to  how
easy  it  is to send data and control signals from the ST.  We  shall  now
move onto simple inputting of data but before we do another small  circuit
needs to be built.

Components list for Input switch module

1 stripboard 10 strips x 15 holes
1 octal DIL switch
1 16-pin DIL socket
1 100k 9-pin SIL resistor network
wire and connectors for data and power lines.

See picture file..PROJECT2.PC3..(<SCREENS folder) for layout.

Double up on the quantity for 16-bit inputs.

     Connect  the  new  circuit  to your interface  unit  or  directly  to
printer  port and set DIL switches in the OFF position.  Now type  in  and
run the following GFA BASIC V3.6 program:-

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

~XBIOS(29,$DF)     !Resets  strobe line low to  switch  suggested  printer
port                   !interface to input mode.
r|=XBIOS(28,0,$0F)!switches  printer port data lines to input  and  places
!data in r|
PRINT "Data on input port reads";r|
PRINT "Press any key to exit"
~INP(2)
~XBIOS(28,0,$8F)  !  Reset  printer port to output as  per  normal  system
! setting
END

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Cartridge  port  users  should use  r%=DPEEK(&HFB0000)  instead  of  XBIOS
routine

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

     The  program should display a zero indicating all input lines are  at
logic  0.  If  you now switch any amount of the switches on  and  run  the
program  again  the screen will display the decimal number  equivalent  of
the  switch settings.  The switches that are in the on position  sets  the
relevant input line (logic 1).  For example,  if the switches on D7,  D3 &
D0  input  lines are on and the rest are off the  binary  number  10001001
will be present at the input port.  Running the above program will display
137, the decimal equivalent.
     It  would be very useful to be able to combine the input  and  output
of data i.e.  monitor the input signals,  process them and then output  as
required.  This cannot be done by direct connection to the printer port as
the 8-bit data lines can only be set for input or output,  they cannot  be
mixed.  I  therefore suggest that the circuit outlined or similar  in  the
last  installment is used.  Cartridge port users are ok as separate  input
and  output  lines  are available.  See  previous  digital  junctions  for
further information.

     Carrying  out input and output of data together is  straight  foward.
Connect  the LED module into your output port,  the switch module  to  the
input  port and run the program listed below.  The program  simpley  reads
the input port,  prints the decimal and hex value on screen then  displays
the binary value on the LED module.

INPUT/OUTPUT Program.

~XBIOS(29,$DF)    !strobe low - interface port to input mode
r=XBIOS(28,0,$0F) !data in and store in r
PRINT "DATA ON INPUT READS ";r,HEX$(r)
~XBIOS(30,$20)      !strobe   high  -  interface  port  to   output   mode
~XBIOS(28,r,$8F)  !output data
END

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

     This  program  can be placed in a loop to save having  to  constantly
run it every time you change the switch pattern, I leave that to you.

     The above example is really no more than a glorified switch but  does
demonstrate  the basic principles.  The last example for this  installment
is  a little more sophisticated.  It demonstrates the principles of how  a
computer  can  be  used to continuously monitor its input  port  and  only
react  when a certain code is received,  rather like an  electronic  coded
lock.

Lock program

code=143           ! or any number between 0 and 255
REPEAT
~XBIOS(30,$20)     ! strobe high
~XBIOS(28,255,$8F) ! set all LEDs on
DELAY 0.5          ! delay for half second
~XBIOS(28,0,$8F)   ! all LEDs off
~XBIOS(29,$DF)     ! strobe low
~XBIOS(28,0,$0F)   ! read input
UNTIL r=code
~XBIOS(30,$20)     ! strobe high
~XBIOS(28,255,$8F) ! set all LEDs on
SOUND 1,15,1,4,20
SOUND 2,15,4,4,20  ! make a noise
SOUND 3,15,8,4,20
WAVE 7,7,0,65535,300
PRINT "YOU MAY NOW ENTER"
PRINT
PRINT "PRESS ANY KEY TO EXIT PROGRAM"
~INP(2)
~XBIOS(28,0,$8F)   ! all LEDs off
END

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

     This  program flashes the LEDs and monitors the input port.  As  soon
as  the  input data,  set by the switches,  matches the number  stored  in
variable 'code' (143 decimal or 10001111 binary  i.e.  switches for  lines
D7,D3,D2,D1,D0  set  on all others off in our example) the  program  exits
the REPEAT - UNTIL loop,  sets all the LEDs on, makes a noise and displays
a message.

     Well thats it for this issue.  I hope you have found the examples and
circuits easy to follow,  I have tried to keep things simple.  If you have
any  problems  then please get in touch.  The program listings  have  been
kept to the bare minimum in order that you can see whats going on,  if you
want  to write your own with GEM buttons etc then do so there  is  nothing
stopping  you.  Also don't be afraid to experiment,  how about  writing  a
program  to  simulate traffic lights at a junction using the  switches  to
simulate the induction loop vehicle sensors buried in the road.

Next Issue
----------     I  hope to discuss the methods required to  enable  control
of  filement  lamps  (as opposed to LEDs) and  electric  motors  including
stepper motors.

Notice Board
------------    Unless otherwise stated, all  modifications,  experiments,
hardware  and  software  discussed in this column are tested on  a  1  Meg
Atari  STFM  with  high resolution  monitor.  However,  the  projects  and
software should work on most other set ups as I have tried to keep  things
to standard.

     If  you  should spot an error or know of a better  way  of  achieving
something  be  it  with hardware or software then please let  me  know  so
that  I  may  pass the knowledge on through this  column.  What  may  seem
obvious  to you may have been over looked by others and could be just  the
answer they are looking for.


     STEN  is  here because enthusiasts are willing to pass on  what  they
know.

Important bit
-------------     Whilst every effort has been made to make sure that  the
information  given  in this article is correct neither I or  STEN  can  be
held  responsible for any damage which may arise due to  readers  carrying
out  modifications  or connecting any devices directly  or  indirectly  to
their computers.

                                             "By order of der Management"

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Bibliography - Suggestions for further reading                        +
+                                                                       +
+ ------------                                                          +
+                                                                       +
+ Concise Atari ST 68000 Referance Guide by K.D.Peel                    +
+                                                                       +
+ Atari ST Internals by Bruckmann, English & Gerits                     +
+                                                                       +
+ GFA BASIC V3.6 Manual                                                 +
+                                                                       +
+ Microprocessor Interfacing by R.E.Vears                               +
+                                                                       +
+ Interfacing your BBC Microcomputer by R.Morgan, W.McClean & J.Rosell  +
+                                                                       +
+ Practical Digital Electronics Handbook by Mike Tooley                 +
+                                                                       +
+ Introducing Atari ST Machine code by Roger Pearson & Sean Hodgson     +
+                                                                       +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

**************************************************************************
*                                                                        *
* Dave Price, 42 Foxglove Green, Willesborough, Ashford, Kent. TN24 0RJ  *
*                                                                        *
**************************************************************************