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Assassins 3 - The Ultimate Games CD (1997)(Weird Science)[!][Amiga-CD32-CDTV].iso
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serial.doc
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1996-08-13
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SERIAL CONNECTIONS
How to connect almost everything -by Mark J Swift and Simon N Goodwin.
A tricky business?
If you have ever tried to connect two pieces of hardware via a serial
interface, you will know that things can get pretty tricky. The problem
is compounded by the fact that no matter how many leads you have made
up in the past, making a new one is like starting from scratch.
With a little advance planning however, making up a lead can be as simple
as putting together a two-piece jigsaw...
Thes files explain in words and pictures how you can make cheap and
reliable connections between many Sinclair computers, near relatives like
the Thor XVI and SAM, and other common machines like Amiga, Atari ST,
Amstrad PCW (with CPS add-on) and PC-compatibles.
The accompanying .IFF files show the connections for common serial ports
on Spectrum and other machines. The files for Spectrum 128 (also QL SER1)
and Interface 1 should be self-evident. The others contain the pin-outs
for D-type serial ports, as used on Amiga, Atari ST, most Amstrads and
IBM-compatibles. The 25 pin variant is used on older PCs, Amiga, ST, PCW,
TRS-80 etc. The DB9 variant is used on SAM's optional Communications
interface, recent PC clones and many laptop and portable computers,
The JIGSAW solution
Each of the accompanying diagrams is drawn as a single piece of a two-piece
jigsaw. To discover the cable connections required to connect two machines,
simply take the relevant pieces - and snap them together!
Other variations
Not all the machines have their own picture - for instance, ST, Amiga and
Amstrad PCWs all use the same 'standard' 25 pin connection. This was the
old RS-232 'standard', used on old PCs, TRS-80s and many terminals. This
fell out of favour because of the bulky connector with a large number of
unused pins, sometimes assigned to conflicting 'extra' signals, and rather
confusing names for the signals.
Some 'AT' PCs and add-on serial boards for various micros replace the
25 way connector with a nine pin connector wired as for the SAM, but with
the addition of DSR on pin 6 and a small voltage, usually between 5 and 9
volts, on pin 7. This is nominally RTS, but finds its most common use
providing power for a serial mouse! You can connect a PC mouse to SAM's
Communications interface if you supply +5V on this pin, but you need to
poll the serial port about every 7 mS or characters get lost, and this
makes it inpractical for use with many SAM programs.
Making your own pieces
If you have a machine that is not featured here then you will need to make
up a jigsaw piece of your own. You should be looking for which lines
are DATA and which lines are HANDSHAKE. You should also take note
of the GROUND line and whether the signal lines are INPUT or OUTPUT.
It is wise to leave power connections, usually marked +5V or similar,
well alone, as these are not needed for serial communications between
computers and are most likely to cause damage if wrongly connected.
If your machine does not match any listed here - and many with 9 pin
or 25 pin D connectors correspond to the SAM and DTE diagrams - you need
to copy the diagram from one of these machines and replace the signal
lines with corresponding ones for the new machine. In the manufacturers
notes, the machine will be described as either DTE or DCE, and this will
determine whether a line is input or output.
DTE devices
'Data Terminal Equipment' is generally intillegent equipment such as
Computers, Terminals and Printers. There should be at least FIVE signal
lines as follows:
TxD (output) / CTS (input) / GND / RxD (input) / DTR (output)
Note that both SAM and Spectrum Interface 1 are DTE devices, but SAM
requires a female connector and the Interface 1 expects a male plug.
DCE devices
'Data Communication Equipment' is generally dumb equipment such as modems,
but the second QL serial port SER2 falls into this category. The signal
names are taken from the intelligent end, so you will find for example
that the Transmit Data (TxD) line is actually an input! This was one of
the most confusing aspects of the original RS-232 serial standard. Again
there will be at least FIVE signal lines as following:
TxD (input) / CTS (output) / GND / RxD (output) / DTR (input)
In a rare moment of standardisation, Sinclair used the same connector and
pinout for the Spectrum 128K and QL SER1. We have successfully used cables
and serial-to-parallel converters made for the QL with original 128K and
Plus Three Spectrums. Note that the QL's SER2 port is differently wired -
it uses the DCE standard rather than DTE.
Further information
This article is based on graphics and text released as part of the Amiga
Qdos Emulator, so you can find machine readable files of the diagrams - in
monochrome packed IFF format - on the Amiga Qdos 3.20 SOURCE disk, in the
sub-directory SerialConnections.
The authors would bve interested to hear of details for third-party
Spectrum serial interfaces such as the Swift Disc, Rotronics Wafadrive,
and any others that may be in your collection. Please send details so
that we can prepare graphics for these as well.
Other aspects
This text has concentrated on hardware connections and skipped over
software. See the documentation for ZXMIT for a tried and tested way
to link a Spectrum and Amiga, and use this data when you wish to transfer
Spectrum files from more esoteric sources - almost every machine has a
Spectrum emulator, these days! In general you should make sure that both
ends of the link are using the same speed and data size. Most machines
default to 9600 baud and 8 data bits, with one or two stop bits. Extra
stop bits do no harm.
You may need to reduce the rate (at both ends) for flakey interfaces -
particularly if you are not using hardware handshaking or transmitting
to a Sinclair machine. Many links can work at 1200 baud or lower speeds
with no need for handshaking.
While we cannot sort out your serial communications problems on an
individual basis, these articles should at least ensure that you get
the connections right. If you run into configuration problems you
should consider writing a letter to William - it's quite likely that
one of the other users has encountered your problem and found a way
round it. If you do write in, be sure to include full details of the
software configuration commands and menu selections that you've tried
at each end of the link. Good luck, and happy handshaking!
M.J.SWIFT April 1993, revised and extended by Simon N Goodwin 1994-1995.