Date: Thu, 20 Oct 1994 11:07:00 +0100
From: [email protected] (Klaus Hegemann)
Subject: Re: Using Auxiliary Port as Serial Port
Message-ID: <b1990b05%[email protected]>
References: <[email protected]>
Newsgroups: comp.sys.amiga.cd32
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Hi Stan !
s> I understand that you can use the auxiliary port (keyboard) as an
s> RS-232 port and that this is what sernet does. But when I look at
s> the pinout, there is only clock and data signals, not ser-in and
s> ser_out. What am I missing here?
Well, I think you refer to the A4000's kb.jack pinout. It's 'almost'
the same as you can find at the cd32. But the difference is, tataa..:
on the cd32 there are additional serial-interface-signals connected
to the AUX-jack. You can find them at the former unused pins.
The mess is, that the (serial-) signals carry [negated] TTL-level.
As a result, you have to make sure that there is a level-conversion
before you connect them to other computers. Without you surely kill
your cd32.
The cd32-FAQ shows a rather complex (but quite correct) way to do this.
(Aehm, the level-conv., of course ;-)
If you plan to connect the CD32 with other Amigas then I found out a
rather easyer/cheaper way to solve that:
Amiga |\ | Amiga CD32
TxD o-------| >|---.
level: RS232 |/ | | level: /TTL
-12V..+12V D1 | 0V..+5V
.-.
| |
| | IC1
R1| | '''
`-' ' _ '
| ' | \ '
*------| O-------->o /RxD Pin6
| ' |_/ '
.-. ' '
| | ' '
| | ' '
R2| | ' '
`-' ' '
| ' '
| ' '
| ' '
=== ' '
/// ' _ '
' / | '
RxD o<-------------------O |---------o /TxD Pin2
' \_| '
' '
'''
GND o-----------------------*---------o GND
|
|
' o o '
' |7 14'
| IC1
|
+5V o--------------------'
the pros. and cons. ([1]this solution ./. [2]max232-sol. (->FAQ) )
pros.[1]: easy to solder
cheap
fits within a SUB-D 25 plug
does not consume CD32 +5V power ;-)
cons: 'dirty' solution; i.e. circuitry makes use of the 1488/89 tolerances
you may only connect Amiga-computers to your cd32 when using THIS
[1] circuitry - since they all use the 1488/89 chip set.
PCs 'may' work, too. But interface board must contain 1488/89 chip
set.
I do believe that this will work on all Amigas -I tested it at least
on 3 different Amiga-models, however, there is still no guarantee
that this will work on yours.
However, I use both interface-types since about 6 months. There has
been no problem yet.
s> Also, has anyone made their own connector to the expansion port to
s> pull off the RGB signals? I'd appreciate hearing of your experience.
Yea, does work fine. In use for about 6 months; and still no probs, too.
For details refer to the cd32-faq.
I am not quite sure about the cd32-pin numbers, just take a look in the
faq.
bis den bald
Klaus
[---------------------------------------------------------------------------]
Date: Fri, 21 Oct 1994 14:55:00 +0100
From: [email protected] (Klaus Hegemann)
Subject: Re: [2]Using Auxiliary Port as Serial Port
Message-ID: <b1a112f9%[email protected]>
References: <b1990b05%[email protected]>
Newsgroups: comp.sys.amiga.cd32
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Hi!
'updated info:'
Amiga 500,2000,1200,...
level: RS232
-12V..+12V
|\ | Amiga CD32
TxD o-------| >|---.
Pin2 |/ | | level: /TTL
D1 | 0V..+5V
1N4001 .-.
| |
| | IC1 7400
R1 | | ........
(*) `-' 1: _ :
| ___| \ :3
*--*___| O-------->o /RxD Pin6
| : |_/ :
.-. 2: :
| | : :
| | : :
R2 | | : :
(*) `-' : :
| : :
| : :
| : :
=== : :
GND /// : _ :4
6: / |____
RxD o<-------------------O |____*----o /TxD Pin2
Pin3 : \_|
: :5
:.......
GND o---------------*-----------------o GND Pin3
Pin7 |
| ........
| 7: :IC1
*--:GND :
| 9: :
*--: \ :
|10: |not :
*--: |used:
|12: | :
*--: | :
|13: | :14
`--: / +5V:-.
:......: |
|
|
+5V o---------------------------'
Pin4
shield o=======================! [n.c.] o shield
Pin1
The RS232-TxD-signal carries +12V or -12V level. As the first step
in conversion the diode D1 blocks if the signal drops to -12V.
In this case the voltage divider (R1,R2) is only connected with
GND potential. So the gate input carries GND level, too.
When the RS232-TxD-signal changes to +12V the diode will pass it
through and the voltage divider now provides a +5V-level signal to
the gate input.
The backward conversion consists of simple negation of the cd32's
/TxD signal. In fact there is no level conversion.
While the conversion for the received signal does
work proper with any RS232 opponent, the sended
signal furthermore carries TTL-level.
The opponent hardware tries to regain the TTL-level signal from
its 'RS232' input. The conversion unit handles the provided
pseudo RS232-type signals correct (as we want ist to be:-).
(*) voltage divider R1-R2:
U U = 12V U = 5V
R1+R2 R1+R2 R1+R2 R2
------ = -----
U R2
R2
U
R1+R2
I = 5 mA ==> R1+R2 = ------ = 2400 Ohm
R1+R2 I
R1+R2
(R1+R2) * U
R2
U = 5V ==> R2 = ------------- = 1000 Ohm; R1= 1400 Ohm
R2 U
R1+R2
R1=1500 Ohm
R2=1000 Ohm ==> I=4.8 mA ==> U(R2)=4.8 V .. will be OK
IC1 = 74LS00 (4 NAND gates)
D1 = e.g. 1N4001
have fun !
be careful; I am in no way responsible for any damage that may result.
CU
bis den bald
Klaus [email protected]</pre>
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