Hi Benjamin,

 BC> My confusion over modems and cables was
 BC> prompted by the thought that since
 BC> the c64 does not have a serial or
 BC> parallel port LIKE THOSE ON IBM CLONE PC'S

Thats funny, because the IBM CLONE PC's don't have a CARTRIDGE or USER
port like the C64,  yet that didn't cause me any confusion when I
hooked a modem up to my brothers PC.  ;-)

 BC> perhaps there did exist `special' modems for the c64. O.k. then a

Yes there did, just as there are also "special" modems for the MAC.

 BC> modem is a modem, but a comm port is not a comm port

Now we are getting somewhere.  

 BC> and I have no idea where to get a cable which will allow me
 BC> to plug a modem (let's say a netcomm m7f) into a commodore 64
 BC> serial port.
     ^^^^^^^^^^^
Neither do I.   The C64 SERIAL port is designed for SERIAL DATA to the
disk drives and/or printer.

Methinks a modem should be driven from the RS232 port JUST LIKE THE IBM

 BC> I need a 25pin or 9pin rs232
 BC> female or male end and I imagine a male
 BC> 6pin end like the one on the serial
 BC> cable which would link a 1541 drive to
 BC> the c64. Where do you get these

You don't.

 BC> I have read other posted messages where users have discussed
 BC> successful null modem transfers between
 BC> an IBM PC clone and a c64 using a
 BC> terminal program at both ends, but where
 BC> the hell did they get a cable that
 BC> would plug into the c64????

Lets get back to basics shall we..

A computer whether it be a C64 or a cray super computer or anything in
between consists of nothing more than a CPU  (microprocessor), a bank
of RAM chips, plus input/output chips to allow them to communicate with
the outside world.  ALL computers have this in common.

There are two input/output chips that are also *similar* for ALL
computers..  these are the video display chips (or video card) for
output, and the keyboard driver so you can enter data.  Again, this is
common on all computers.

ALL computers "work" by addressing memory via parallel buss lines..
they CANNOT work any other way.  C64/IBM are both the same in this
respect too.

Now we come to the differences...

Because people wish to use things like printers and modems then OTHER
ports are needed.

Almost all modems have been designed for RS232 operation.
Printers have been designed for either RS232 OR Centronics operation.

NO "computer" will support these without additional chips/cards. All
*any* computer can do is input/output data via its parallel buss.

The PC, because it is an open ended structure can be made to cater for
for RS232 or Centronics (parallel) I/O by plugging in DRIVER cards into
the computers data buss..  these driver cards are interfaces that
converts parallel buss data into an RS232 serial data stream, OR in the
case of Centronics it essentially does little more than add
handshaking. (Unless you are using a 16bit computer, in which case it
will convert the 16bit data to 8 bit data as well).

The C64 is a "closed" structure, and "cards" can't be
just plugged in.
HOWEVER, these cards are not needed because these "extras" are already
built in to the C64 computer.
The SID chip takes the place of the sound card, the USER port caters
for both RS232 AND Centronics (parallel) support via different pins.
The C64 *also* has its own "special" serial port (NOT RS232) for it's
disk drives and/or printer, it also has special ports inbuilt for
joystick, cassette tape, and the CARTRIDGE port is linked directly to
the data buss..  this allows us to make our own "cards" should we ever
need them.

What all this means is that unlike the PC, where to drive an RS232
device an RS232 driver card is the only option, us C64 users already
have an RS232 driver built in..  the signals are available at the user
port..  albeit these signals are only 0-5v rather than the "correct"
+-12 volts..  so although we have the correct DATA at this port we need
a voltage converter. This port however can only supplort low speed.

Because we also have access to the data buss we are not limited to this
internal RS232 support..  we can build a "driver card" to plug into
this buss to *improve* the minor shortcomings of the inbuilt RS232..
this has been done via cartridges such as the HARTCART and Swiftlink.

So in essence, whilst on the PC you only have one option, we have at
least two.

Neither option requires "just a cable" ...  this doesn't work with the
PC's and it doesn't work with the C64..

If you wish to use the USER port and the C64's internal RS232 interface
then you also need to "amplify" these signals.  If you use the
cartridge port option then the "card" will output the correct voltage
levels anyway so just a cable plugged into this interface will do.

Because the choice is *yours* then it is hard to advice on what you
require..  a user port voltage converter kit can be purchased from
Jaycar for about $20 - The CABLE you will need to connect between this
converter and the modem will depend on your modem..  Most modems use a
25 pin "D" connector..  a "Mac" modem uses a mini din connector.
Internally both modems are identical.. only the plug has been changed.

If you opt for the swiftlink or hartcart you still need a cable from
the interface to the modem..  again, this will depend on the
plug/sockets on your mode.

 BC> I have read other posted messages where users have discussed
 BC> successful null modem transfers between
 BC> an IBM PC clone and a c64 using a
 BC> terminal program at both ends, but where
 BC> the hell did they get a cable that

Same as above...   same interface/driver is required.. the cable being
dependent on the interface and the modem itself.

PLEASE NOTE: Hardware/software devices such as X1541 or CNET achieve
this effect  (xferring data from PC/C64) but they don't use RS232 for
communication..  the transfer data directly between the data buss of
both computers (putting it crudely).  Essentially no converters are
required since all computers run at 5v data levels and a serial
conversion (RS232) is not required, you can pass data directly across
the computers data buss..   In this case it is then the software that
controls the data flow, and how this is achieved is entirely up to the
software author.

I'm sorry to rave on as much as I have, but it really is one of my pet
hates when people see computers as something "magical", and especially
when they see a C64 as being totally different from other computers.
Yes, they are different in that many of the "add ons" required for a PC
is actually inbuilt on the C64, but the DATA is the same, the RAM is
the same, the CPU's work the same way.

So other than having more than one choice, why is it so confusing ?

Surely not all IBM users are totally ignorant as to how their machines
operate, and even more surely, given more than one option they don't all
fall into a heap of confusion.. ..  so why do I keep geeting this
feeling that they do ! :-(

Cheers
Rod

PS..  I think that computers should be like cars..  no one is allowed
to drive a formula one racer until that have grasped the fundimentals
and had sufficient experience at "normal" driving..  I don't think
people should be allowed to use "high power" computers until they at
least have a fundimental understanding of how a "basic" computer such
as a C64 works...  it sure would save a lot of people a lot of
headaches if they learned to walk before they start to run.  :-)

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