<GHGALAP@cc1.kuleuven.ac.be> (04/17/91)
Hello dear fellow HP-28 hackers,
Here my experiences on building an RS232 link to the
HP 28S.
I have not yet opened it up but I tried to make a connection trough
the IR link (Only to the computer). It worked, but not entirely the
way it should.
Anyway, a good book is :
VOYAGE AU CENTRE DE LA HP28c/s
Paul Courbis et S{bastien Lalande
PARIS, Editions de la R}gle @ calcul
65, Bd Saint- Ger{ain. BP 300, 75288 PARIS CEDEX
ISBN : 2.90785.601.4
Oh yes, this book is written in FRENCH |||
(I think the french specific characters will be printed wrong)
I don't know if most people on the net understand French, since
most of them are in America (I think).
By the way , most people here in Belgium talk three or four languages
(Dutch, French, English, German). Ain't that unbelievable ?
I think it is more or less the only country in the world where so
many languages are spoken.
Serious now.
hardware :
----------
I connected a fototransistor to a transistor to amplify the signal.
Switching the IR led on and off resulted in a voltage swing from
-5 volt to +5 volt. Connecting this to pin 3 on the RS232 connector
(RxD) and connecting GND to pin 7 (signal ground), the computer
seemed to receive signals. A voltage swing of 0 to 10 V worked too,
0 to 5 V did not (I think actually it should work).
Software :
----------
The following routine takes a "pt" object, so don't call it directly.
Compile it into an IMC called "SEND.OBJ" and use "SEND" to
do the actual sending.
8F18050 CALL.A SaveRegs
8F72F40 CALL.A GetPt
1BD0FFF MOVE.5 IRLED,D0
308 MOVE.P1 #8h,C ; send 8 bits + 1 startbit
816 RRN.W C ; put counter in field S
C4 * loop ADD.A A,A ; shift bit into carry
590 * BRCC zero
302 MOVE.P1 #2h,C
6600 JUMP.3 send
300 zero MOVE.P1 #0h,C
1540 send MOVE.P C,(D0) ; set LED on or off
3162 MOVE.P2 #26h,C ; change this num to change delay
A6E wait DEC.B C
5CF BRCC wait ; delay
A4E DEC.S C
5FD * BRCC loop ; next bit
300 MOVE.P1 #0h,C ; switch LED off
1540 MOVE.P C,(D0)
8D505B1 JUMP.A continue ; continue rpl
'SEND' ?6B0C!
<< DUP TYPE
IF NOT THEN # C53Bh SYSEVAL SEND.OBJ ; 0CB35: real->pt
END DROP
>>
use :
the bits that are to be sent, should be in the left of a 20 bit
integer. For example the character "o" is coded as
o -> ascii code = #6F ; switch nibbles : F6
invert (sending 1 = receiving 0) :F6 -> 09
adding 1 startbit : #109 ; shift left until startbit is most left :
"o" -> #84800 h.
to send an "o" do : #84800h B->R SEND.
I set my computer to 1200 baud, 8 bits,no parity, 1 stop bit.
This routine worked, but the bits are in the wrong order. It takes a
lot of work to correct this (as you've seen above)so I changed
the program to use right shifting in stead of left shift, but It did
not work the way it should. The changes were in the lines
marked with an *.
822 loop CLR SB
819F0 SRB.A A
83290 BRBC SB,zero
570 BRCC loop
I don't know whether it is necessary to clear the SB, but without
this instruction it did not work either.
I suspect there is some problem with the timing, I tried changing it
but it did not work. Can somebody help me : post some timing info
on the ML instructions.
Do I have to switch the interrupts off ? Is it easier to use the
timer to for timing the bits ?
I also had problems with errors that were send trough. Mayby
600 baud is more reliable, but I did not try it. Actually, it was
very difficult to get something correct to the computer. Mayby
I should do some filtering in the electronics or so ? Can somebody
post some info please ?
Anyway, I'm now busy opening my 28, and i'm working on some info
how you should open it. I'll post it as soon as it is ready.
Joris.
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