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Article #71 (75 is last):
From: Michael Current 
Newsgroups: freenet.sci.comp.atari.prog.8bit.resource
Subject: RVerter Type Interface (Instructions)
Posted-By: xx004 (Atari SIG)
Date: Sat Sep 26 17:06:14 1998

From: cp576@cleveland.Freenet.Edu (Kenneth L Siders)
Date: 21 Jan 1995 09:21:28 GMT

How to build a serial interface (up to 19200 baud).

The following is the description of how to build an RVerter compat
interface.  I have never actually seen one so I derived most
of this from tracing the connections inside an SX212 modem to
determine what pins on the SIO interface corresponds to which
on the RS232 connection(except the data lines which are obvious).
This interface should work with any RVERTER(or BOBVERTER)handler.
It may work with SX212 handlers or software but may not support
all of the baud rates.  Handlers are available alone and with
some terminal programs like Bobterm.
I am not sure if all handlers support 19200 baud, but I have
used my interface connected via a null modem cable to an IBM to
transfer files at 19200 baud and have had no problems.  I tried
38400 baud (by patching the handler) and too many errors were
generated.  I also connected by SX212 to the interface instead
of the SIO connection and had no problems.  I actually built this
by lightly super gluing the two ICS into a large DB9 hood and
soldered the connections.  I don't recommend this approach unless
you are totally nuts.  I would NEVER try that again even though
it did work (after fixing a couple mistakes).  I planned on
eventually filling it with EPOXY but I didn't and pray nothing
ever comes loose.  The cable I build has an SIO cable (from my
fried XM301 modem, and the interface build in the other end with
a DB9 male connector.  I was able to use a ready made IBM cable
to connect to the modem.  I also build a null modem cable and
gender changer.  This interface is unable to communicate at the
same time as other I/O is occurring.  This is typical unless
you have an interface that connects to the XL/XE parallel bus.
Note: CTS is not supported so you cannot use RTS/CTS handshaking.
Only XON/XOFF could be used.  When transfering files between
computers, if you use a protocol this will not cause a problem.
No reponsibility is assumed for any damages resulting from
the building or using of this interface.


Parts:
------
IC1      MAX232/ICL232 RS232 Level Converter with onboard
          +10V/-10V voltage generator.
IC2      74LS00 Quad NAND Gate.  Used to disconnect Data Lines
          when DTR is not asserted.
R1       1K resistor 1/4W
R2       4K resistor 1/4W (3K to 7K should be OK)
C1,C2    4.7uF capacitor
C3,C4,C5 10uF capacitor
D1,D2,D3 IN4148 or IN914A or similiar diodes
ZD1      IN4733 5.1V Zener Diode or IN4734 5.6V Zener Diode

I don't have a data sheet for MAX232 and are giving  the values for
the capacitors from another circuit.  I used 33uF caps for all of them
(I have a lot of them I got cheap) and have had no problems.  Place
them as close to IC1 as possible.  They should probably be 12 to 16
volt types or better especially C3 and C4 which see around 10 volts,
where the other three only see 5V.


ASCII Circuit Diagram
---------------------

Atari SIO                                             DB9 male
(connector or                                      (IBM compat.)
cable))
                 +                  +        +
gnd(4)---GND---||--+               +-||-+   +-||-+
               C5  |               | C1 |   | C2 |
+5v(10)---VCC------+           ____|____|___|____|_____
                               |  (1)  (3) (4)  (5)   |
                               |  C1+  C1- C2+  C2-   |
               D1              |                      |
Proceed(9)____[\|______________|(9) R2OUT     R2IN (8)|--(1)CD
              [/|              |                      |
Motor(8)_______________________|(10)T2IN      T2OUT(7)|--(7)RTS
                    |          |                      |
                    |          |                      |
            R1      |          |                      |
      GND-/\/\/\----+          |         IC1          |
                    |          |                      |
           D2  _____|_____     |                      |
Dt.In(2)__[\|__|(6)(9,5)(1)|___|(12)R1OUT    R1IN (13)|--(2)D.IN
          [/|  |        (2)|_/ |                      |
               |           |   |                      |
Dt.Out(5)______|(13)    (8)|___|(11)T1IN     T1OUT(14)|__(3)D.OUT
           \___|(12)       |   |                      |
               |           |   |                      |
             __|(3) IC2    |   | V+  5V   gnd  v-     |
             \_|(4)        |   |_(2)_(16)_(15)_(6)____|
               |           |      |    |   |    |
         GND---|(7)        |      +-||-+   |-||-+--------(4)DTR
               |       (10)|__     +C3     |+C4
         VCC---|(14)   (11)|_/             |       GND---(5)GND
               |___________|              GND


                                   (no connection) NC----(6)DSR
                                                   NC----(8)CTS

Optional (Only needed to be able to detect ring signal from
Modem):   This is not tested, Hopefully it does not need to
be inverted.  You could probably use a 1489 if you know how.
                         D3                     R2
Interupt(13)____________[\|____________________/\/\/\____(9)RI
                        [/|            |
                                   ZD1 |
                      GND__________[\7_|
                                   [/L


Be sure to note polarity of capacitors.  Note: The positive
lead of C4 does go to ground since the other leg will be a
negative voltage.  + and /  \ are use to show connections and
bring connections together on the diagram.  Sorry not to break
the ICs down into parts but that would have made the diagram
worse.

Pins for RS232 are for a 9 pin connector.  With this connector
you can connect a standard 9 to 25 pin cable to this connector
to use a modem, or a null modem cable to transfer files.  You
can substitute a 25 pin connector using table below.  If you
plan on only using it for file transfers you can wire in the
null modem cable before the jack.  Note: The 9 pin connections
are not the same as the 850 interface but are the same as used
sometimes on IBM type computers.  Change the gender of the plug
as desired.

9 Pin   25 Pin
--------------
  1       8
  2       3
  3       2
  4      20
  5       7
  6       6
  7       4
  8       5
  9      22

RS232 Definitions:
------------------
CD=Carrier Detect (inp)       DTR=Data Terminal Ready (out)
D.IN=Data In(inp)             D.OUT=Data Out (out)
DSR=Data Set Ready (inp)      CTS=Clear to Send(inp)
RI=Ring Indicator (inp)

Null Modem connections
----------------------
This is for 9 pin connectors, if a 25 pin connector is used
use chart earlier to convert.
Connect pin 5 straight through.
cross in one end of the cable 2 with 3 and 7 with 8.
connect 1,4, and 6 in each end of the cable.

  If you are only using the interface for computer to computer
transfers, you can build this into the interface if you are
careful.  Connect what would go to pin 3 to pin 2.  Connect what
would go to pin 3 to pin 2.  Connect what would go to pin 8
to pin 7.  Connect 1,4,6 together on the connector.  Connect what
would go to pins 1 and 4 together.  Connect pin 5 normally.

Parts Sources
------------
  Resistors, capacitors, diodes should be available from Radio
Shack (not sure about the zener diode if you need it).  The
DB9/DB25 connectors and hoods should also be available there.
Atari SIO cables are available from one of the Atari Dealers -
just remove one end.  You may also want to pick up a prototyping
board at Radio shack to build it on.
  I got the MAX232 for $1.65 and 74LS00 for 22 cents at BG Micro.
(US$ only,$10 minimum order on credit cards) $3.25 minimum shipping
($7.50 Canada, $15 others, no shipping to Mexico or Puerto Rico).
You could also get IN4148 diodes at 100/2.50. Other items that
you could get to pad an order if you need them:
14 pin socket  13/1.00 (only need 1),16 pin sockes  13/1.00
(only need 1), 6821 PIA $2.00  (same as 6520?), 6810 (used in
1050) $1.25, 2793 (Controller used in 1050) $7.50, 4164-150ns RAMS
at $0.49 or 9/3.50, 41256-150ns RAMs at $1.25 or 9/9.95 (256Kx1),
62256 32x8 SRAM $5.00 (can this upgrade the Black Box as
described in the last issue of the original A.C.?) Orders 1-800-
276-2206, Tech suport 214-271-9834, Fax 214-271-2462.  P.O.
Box 280298 Dallas, TX 75228.  This along with a couple other
places was listed in one of the original A.C. issues.

Last Update 1/95

Send corrections and typos to cp576@cleveland.freenet.edu




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