use com port as parallel port

[b3ny]

hello everybody, short question
is it possible to use the serial com port with the comm api as
parallel port
and check every single input channel (if it is high)??

i'am trying to create a extern media controller, that has buttons for
play, stop, next,volume up... and i want to keep everything
simple(without parallel/seriell converter)...

thanx 4 help beny

 

[Graeme Hill]

I think you have the wrong end of the stick here.

Com ports are serial devices i.e. one bit at a time, one after the other.
You would needs some extra electronics to interface what you describe to a
serial port - parallel and serial ports are electronically and
theoretically different in design and practice.

If you did want to interface such a controller to a serial port, you would
need to conver the switch activations to a serial byte of information
that could pass back to the serial port.

 

[b3ny]

I think you have the wrong end of the stick here.

i knew thus... but the serial port has more than one in/output channels...
RxD and TxD are the two data channels, but whats up with the status bits??
DCD DSR RTS CTS and DTR can't i use them as normal in/outputs???

beny

 

[Oscar kind]

i knew thus... but the serial port has more than one in/output channels...
RxD and TxD are the two data channels, but whats up with the status bits??
DCD DSR RTS CTS and DTR can't i use them as normal in/outputs???

No. These bits are used by the serial port controller (i.e. the hardware)
to control when to send bits over the communication wires. After all, the
buffers on both sides must not overflow.

Even though the software can tell the controller which handshaking
protocol to use (i.e. the pins or using special bit patterns on the
communication line), the controller is in charge. Not the software.

 

[Knute Johnson]

i knew thus... but the serial port has more than one in/output channels...
RxD and TxD are the two data channels, but whats up with the status bits??
DCD DSR RTS CTS and DTR can't i use them as normal in/outputs???

beny

yes you can!

 

[Babu Kalakrishnan]

No. These bits are used by the serial port controller (i.e. the hardware)
to control when to send bits over the communication wires. After all, the
buffers on both sides must not overflow.

Even though the software can tell the controller which handshaking
protocol to use (i.e. the pins or using special bit patterns on the
communication line), the controller is in charge. Not the software.

That isn't quite right - at least for the 16450/16550 compatible serial
ports that are used in the IBM PC architecture. Flow control must always
be performed by software - (The nomenclature "Hardware" vs. "Software"
flow control only differentiates between whether the signalling of these
states is done through the hardware pins RTS/CTS or as part of the data
stream - XON/XOFF)

So while you cannot control the state of the TxD pin (or read that of
the RxD pin) programmatically, all the remaining pins (DTR and RTS as
outputs and DSR,CTS,DCD and RI as inputs) can be controlled / read
asynchronously from the PC.

 

[b3ny]

So while you cannot control the state of the TxD pin (or read that of

the RxD pin) programmatically, all the remaining pins (DTR and RTS as
outputs and DSR,CTS,DCD and RI as inputs) can be controlled / read
asynchronously from the PC.

tell me how it works???
how di i have to config the comm api?
maybe a little source code example?

thanx beny

 

[Babu Kalakrishnan]

tell me how it works???
how di i have to config the comm api?
maybe a little source code example?

Check out the API for the javax.comm.SerialPort class. You have the
setDTR(), setRTS() methods to set the output bits and the
isDSR(),isCTS(), isCD(), isRI() methods for reading the bits.

BK

 

[Graeme Hill]

Please remember that according to the RS232 specification, a 1 (high bit)
is a NEGATIVE voltage with respect to ground - between perhaps -5 and -15
volts. A 0 (low bit) is POSITIVE with respect to ground, again e.g. +5 to
+15 volts.

Paralell ports, on the other end, will typically operate at TTL voltages
e.g. 0 V is 0(low) bit, +5V is 1(high) bit.

If you don't know what you doing, you will almost certainly fry your RS232
port.


More info e.g. http://www.sangoma.com/signal.htm

 

[steve]

Please remember that according to the RS232 specification, a 1 (high bit)
is a NEGATIVE voltage with respect to ground - between perhaps -5 and -15
volts. A 0 (low bit) is POSITIVE with respect to ground, again e.g. +5 to
+15 volts.

Paralell ports, on the other end, will typically operate at TTL voltages
e.g. 0 V is 0(low) bit, +5V is 1(high) bit.

If you don't know what you doing, you will almost certainly fry your RS232
port.


More info e.g. http://www.sangoma.com/signal.htm

there is not enough wires, to cover all his options , unless he implements
some external logic.

he has a number of options.

1. give up
2. use the parallel port.
3. use the usb port with a couple of extra chips.
4. if he insists on using the serial port, he just needs a parallel to serial
convertor chip.
then feed his signals into the parallel side.
he can use the chip to handle the RS232 interface

Then use 2 other control lines 1 to reset the chip & 1 to act as a clock. (
unless the chip implements it own internal clock)

first step , each time he wants to read.
1. issue a reset signal to the external chip ( puts the parallel chip in
exactly a known state)
2. issue a clock signal to clock the data out, until 1 byte received.
allow the api to assemble the byte.
3. read byte , decode bits.
go to 1.

he does not even need a voltage convertor. to get his +- supply. if he is
smart he can leach off the RS232 port. ( set 1 line high , & 1 line low then
use that to power the chip & circuit ( cmos))

 

[Ann]

there is not enough wires, to cover all his options , unless he implements
some external logic.

he has a number of options.

1. give up
2. use the parallel port.
3. use the usb port with a couple of extra chips.
4. if he insists on using the serial port, he just needs a parallel to serial
convertor chip.
then feed his signals into the parallel side.
he can use the chip to handle the RS232 interface

Then use 2 other control lines 1 to reset the chip & 1 to act as a clock. (
unless the chip implements it own internal clock)

first step , each time he wants to read.
1. issue a reset signal to the external chip ( puts the parallel chip in
exactly a known state)
2. issue a clock signal to clock the data out, until 1 byte received.
allow the api to assemble the byte.
3. read byte , decode bits.
go to 1.

he does not even need a voltage convertor. to get his +- supply. if he is
smart he can leach off the RS232 port. ( set 1 line high , & 1 line low then
use that to power the chip & circuit ( cmos))

You can also get a USB to Centronix 36pin printer cable
that will convert USB to parallel. I saw one at a store for $20.
I bought a serial to parallel converter a few years back, maybe $35
but prices have probably dropped.

 

[Babu Kalakrishnan]

Graeme Hill wrote:

Please do not top post.

Please remember that according to the RS232 specification, a 1 (high bit)
is a NEGATIVE voltage with respect to ground - between perhaps -5 and -15
volts. A 0 (low bit) is POSITIVE with respect to ground, again e.g. +5 to
+15 volts.

Paralell ports, on the other end, will typically operate at TTL voltages
e.g. 0 V is 0(low) bit, +5V is 1(high) bit.

I was assuming that the OP knows what he's doing wrt signal levels and
polarities since he mentioned he was building the hardware.

If you don't know what you doing, you will almost certainly fry your RS232
port.

If you try connecting an RS-232 signal directly to a TTL device, the
more likely candidate to get fried is the TTL side - not the RS-232 port
A TTL input signal level is well within RS-232's defined input range (If
the RS232C side is the input), and its output drivers are expected
to be current limited / short circuit protected.

BK