Interfacing Spartan 3 board to PC parallel port??

Hello,
I have been working on a project and the submission date is
due very soon. Now I am having some problems which need to be
addressed. Here I go,

I am using digilent Spartan 3 board for my project. My
project needs to operate on the data sent by PC. I am using PCs
parallel port to send and receive data. (I have a code written in C
which uses outportb() and inportb() to exchange data. on the otherside
in VHDL i have a data bus which is bi-directional.. inout... )

now the problem is the voltage levels these two operate at. FPGA
operates at 3.3V and parallel port uses 5V to represent logic values...

I saw a parallel I/O board (PIO1) on digilent website, but now have no
time to order one...

So what is the best way to construct a simple interface which can be
used.
Also can I directly connect the PC parallel port to spartan 3 boards
expansion slot??
if no, please suggest me a simple interface (some level shifter which
has to be bi-directional, or alternate solution) which I can use...

I need something similar to the digilent POI1 board.
http://www.digilentinc.com/Products/...Nav2=Accessory

Can i construct this board and use it? (ofcourse without the JTAG
module) if yes, please tell me in this schematic
http://www.digilentinc.com/Data/Prod...odPio1_sch.pdf what is
IC2. seems like a voltage regulator. but can you tell me which
regulator is this?
I feel i can construct this interface which consists of voltage
dividers, this voltage regulator and connections.. but please tell me
whether this will work for bi-directional data???

waiting for your reply
thankyou
Shailesh.

[email protected] wrote:
> Hello,
> I have been working on a project and the submission date is
> due very soon. Now I am having some problems which need to be
> addressed. Here I go,
>
> I am using digilent Spartan 3 board for my project. My
> project needs to operate on the data sent by PC. I am using PCs
> parallel port to send and receive data. (I have a code written in C
> which uses outportb() and inportb() to exchange data. on the otherside
> in VHDL i have a data bus which is bi-directional.. inout... )
>
> now the problem is the voltage levels these two operate at. FPGA
> operates at 3.3V and parallel port uses 5V to represent logic values...
>
> I saw a parallel I/O board (PIO1) on digilent website, but now have no
> time to order one...
>
> So what is the best way to construct a simple interface which can be
> used.
> Also can I directly connect the PC parallel port to spartan 3 boards
> expansion slot??
> if no, please suggest me a simple interface (some level shifter which
> has to be bi-directional, or alternate solution) which I can use...
>
> I need something similar to the digilent POI1 board.
> http://www.digilentinc.com/Products/...Nav2=Accessory
>
> Can i construct this board and use it? (ofcourse without the JTAG
> module) if yes, please tell me in this schematic
> http://www.digilentinc.com/Data/Prod...odPio1_sch.pdf what is
> IC2. seems like a voltage regulator. but can you tell me which
> regulator is this?
> I feel i can construct this interface which consists of voltage
> dividers, this voltage regulator and connections.. but please tell me
> whether this will work for bi-directional data???
>
> waiting for your reply
> thankyou
> Shailesh.
>


Why not just use the RS-232 port?

Eli Hughes wrote:
> [email protected] wrote:
> > Hello,
> > I have been working on a project and the submission date is
> > due very soon. Now I am having some problems which need to be
> > addressed. Here I go,
>
> Why not just use the RS-232 port?

Because his homework assignment was to use the parallel port.

-a

Andy Peters <[email protected]> wrote:
> Eli Hughes wrote:
> > [email protected] wrote:
> > > Hello,
> > > I have been working on a project and the submission date is
> > > due very soon. Now I am having some problems which need to be
> > > addressed. Here I go,
> >
> > Why not just use the RS-232 port?

> Because his homework assignment was to use the parallel port.

Perhaps he needs to acchive datarates far above 1MB?

--
Uwe Bonnes [email protected]

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

Andy Peters <[email protected]> wrote:
> Eli Hughes wrote:
> > [email protected] wrote:
> > > Hello,
> > > I have been working on a project and the submission date is
> > > due very soon. Now I am having some problems which need to be
> > > addressed. Here I go,
> >
> > Why not just use the RS-232 port?

> Because his homework assignment was to use the parallel port.

Perhaps he needs to acchive datarates far above 1MBaud?

--
Uwe Bonnes [email protected]

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

[email protected] wrote:
> Hello,
> I have been working on a project and the submission date is
> due very soon. Now I am having some problems which need to be
> addressed. Here I go,
>
> I am using digilent Spartan 3 board for my project. My
> project needs to operate on the data sent by PC. I am using PCs
> parallel port to send and receive data. (I have a code written in C
> which uses outportb() and inportb() to exchange data. on the otherside
> in VHDL i have a data bus which is bi-directional.. inout... )
>
> now the problem is the voltage levels these two operate at. FPGA
> operates at 3.3V and parallel port uses 5V to represent logic values...
>
> I saw a parallel I/O board (PIO1) on digilent website, but now have no
> time to order one...

Series resistors ( wire between M-F DB25 as a cascade connector )
should be good enough. Add clamp diodes if you like.
You only need microsecond region times, and probably do not care
about power loss.

-jg

Jim Granville wrote:
> [email protected] wrote:
> > Hello,
> > I have been working on a project and the submission date is
> > due very soon. Now I am having some problems which need to be
> > addressed. Here I go,
> >
> > I am using digilent Spartan 3 board for my project. My
> > project needs to operate on the data sent by PC. I am using PCs
> > parallel port to send and receive data. (I have a code written in C
> > which uses outportb() and inportb() to exchange data. on the otherside
> > in VHDL i have a data bus which is bi-directional.. inout... )
> >
> > now the problem is the voltage levels these two operate at. FPGA
> > operates at 3.3V and parallel port uses 5V to represent logic values...
> >
> > I saw a parallel I/O board (PIO1) on digilent website, but now have no
> > time to order one...
>
> Series resistors ( wire between M-F DB25 as a cascade connector )
> should be good enough. Add clamp diodes if you like.
> You only need microsecond region times, and probably do not care
> about power loss.
>
> -jg

If I remember correctly, I remember reading about connecting 3.3V CMOS
configuration output signals to Xilinx 2.5V CMOS inputs and that was OK
as long as the current limit (series resistor) limited the current to
less than 10 mA. I think that was for Virtex II. I then remembered
that the Spartan3 3.3V CMOS inputs are sensitive to overvoltage due to
the 0.9 micron technology. There may be issues connecting 5 volt
logic to Spartan3 3.3 volt inputs with series resistors. I think I
remember someone saying that the IBIS model will tell you what the
delta V of the input clamp diode will be at various input currents.
Also consider that if the 3.3 V supply is lightly loaded, the 5 volt
signals may have a sneak path through the assumed input clamp diodes
and raise the 3.3 volt power supply above 3.3 volts.

jg: Were the input clamp diodes to address the 0.9 micron issue, or the
possible lack of an intrinsic input protection diode?

- Newman

oops, it is not 0.9 micron but 90 nanometers.

Shailesh: You might also double check to see that the parallel port
accepts TTL level inputs and not regular 5 Volt HC input levels.

-Newman

I have to stick to parallel port!!!

@newman,
about connecting 3.3V to 5v parallel port(vice versa), can I use
some form of voltage dividers???
I need a configuration which is bi-directional..

This is very basic, remember the old masters;

Ohm and Thevenin

add

FPGA datasheet
EPP/ECP specification

think...

[email protected] wrote:
> I have to stick to parallel port!!!
>
> @newman,
> about connecting 3.3V to 5v parallel port(vice versa), can I use
> some form of voltage dividers???
> I need a configuration which is bi-directional..

yes, but keep in mind a parallel port might use 3.3V output, so
design it so it will work on 3.3V and 5V PPorts.

-jg

Jim Granville schrieb:
> [email protected] wrote:
>
>> I have to stick to parallel port!!!
>>
>> @newman,
>> about connecting 3.3V to 5v parallel port(vice versa), can I use
>> some form of voltage dividers???
>> I need a configuration which is bi-directional..
>
>
> yes, but keep in mind a parallel port might use 3.3V output, so
> design it so it will work on 3.3V and 5V PPorts.

The parallel port uses TTL levels. You must accept anything above 2.0V
as high, and anything below 0.8V as low.

Many parallel ports get very slow rise times above 1.6V, therefore the
lower the threshold voltage the better. Using 2.5V CMOS IO on the FPGA
with a series resistor to limit the 5V current should work fine with a
threshold of 1.25V

3.3V CMOS IO gets you a threshold of 1.65V where the signals are
dangerously flat allready. In that case you should add a schmitt
trigger. You can build a schmitt trigger by using two FPGA pins per
input. A resistor between the two pins and a resistor between one pin
and the input allows you to feed back the received value to the input.

Kolja Sulimma