Parallel port hardware

[petrus bitbyter]

Yes, this is the main problem. Sure I can program it so its high through
the programming but I'd rather not take that chance in general. I'm not
quite sure how to handle this. The problem is with the pic though. I could
add a resistor to limit the current but then it will reduce the voltage.
Although it might not matter to much.

I send an schematic to alt.binaries that shows the idea I'm looking at.

Thanks,
Jon.

Did not find the collission detection but I think the circuit below will
prevent any output to be blown providing the level shift you need at the
same time.

----+-------+-----+--5V
| | | --+---+--2.5V
.-. .-. | | |
| | 10k| | | .-. .-.
| | | | | | | | |
'-'4k7 '-' | 10k| | | |56k
| | | '-' '-'
| | |\| | |
| +---|-\ ___ | | PIC
SPP | | | |-----|___|--+--)---+------
----+-+-----)---|+/ 2k7 | | I/O
control| | |/| | |
| | LM339 | |
| | | | |
| | | /| | |
| | | /+|--+ |
+-----)-----)-------| | |
| | \-|-----+
| | \| |
| | LM339 |
.-. | .-.
| | | | |
10k| | | 10k| |
'-' | '-'
| | |
| | |
------------+-----+----------------+---------
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Any PIC I/O pin I am aware of can sink and source at least 1mA. So the 2k7
resistor being the maximum load will prevent damage from I/O current. At the
same time, the input leakage current on a PIC input pin is in the uA range.
So the 56K will prevent the input to become floating when the output goes
tri-state. Some PICs can activate weak pull ups to do the same.

petrus bitbyter

 

[Gary Tait]

There used to be a standard 'mod' for the old printer cards, of cutting
pin1 on the output driver chip (the output enable line), and connecting
it to a spare latch on an LS174 on the card, allowing the direction to
be switched.
The outputs on the parallel port, were _not_ 'open collector' drives.

Best Wishes

I've done that one before. You use bit 5 on the control line.

I've also made a paralell card into an interface for one of those
MKE/Panasonic/Creative CD-ROM drives.

 

[JosephKK]

petrus bitbyter [email protected] posted to
sci.electronics.design:

Did not find the collission detection but I think the circuit below
will prevent any output to be blown providing the level shift you
need at the same time.

----+-------+-----+--5V
| | | --+---+--2.5V
.-. .-. | | |
| | 10k| | | .-. .-.
| | | | | | | | |
'-'4k7 '-' | 10k| | | |56k
| | | '-' '-'
| | |\| | |
| +---|-\ ___ | | PIC
SPP | | | |-----|___|--+--)---+------
----+-+-----)---|+/ 2k7 | | I/O
control| | |/| | |
| | LM339 | |
| | | | |
| | | /| | |
| | | /+|--+ |
+-----)-----)-------| | |
| | \-|-----+
| | \| |
| | LM339 |
.-. | .-.
| | | | |
10k| | | 10k| |
'-' | '-'
| | |
| | |
------------+-----+----------------+---------
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Any PIC I/O pin I am aware of can sink and source at least 1mA. So
the 2k7 resistor being the maximum load will prevent damage from I/O
current. At the same time, the input leakage current on a PIC input
pin is in the uA range. So the 56K will prevent the input to become
floating when the output goes tri-state. Some PICs can activate weak
pull ups to do the same.

petrus bitbyter

Tends to get stuck at "0" doesn't it?

 

[petrus bitbyter]

petrus bitbyter [email protected] posted to
sci.electronics.design:


Tends to get stuck at "0" doesn't it?

You're right, this circuit will not work. I'll have a second look tomorrow
(if I find some time)

petrus bitbyter

 

[petrus bitbyter]

You're right, this circuit will not work. I'll have a second look tomorrow
(if I find some time)

petrus bitbyter

----+-------+-----+-5V
| | | +--------------+--2.5V
.-. .-. | | |
| | 10k| | | .-. .-.
| | | | | | | | |
'-'4k7 '-' | | |560k | |56k
| | | '-' '-'
| | |\| | 2k7 |
| +---|-\ | ___ | PIC
SPP | | | |-----+--+-|___|--+--+------
----+-+-----)---|+/ | | I/O
control| | |/| | |
| | LM339 | |
| | | | |
| | | /| | |
| | | /-|--+ |
+-----)-----)---| | | |
| | \+|--)--------+
| | \| | |
| | LM339 | |
.-. | .-. |
| | | | | |
10k| | | | |560k |
'-' | '-' |
| | | |
| | | |
------------+-----+---------+--------+-----
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Modified circuit. This one will work... unless I made another mistake

petrus bitbyter

 

[JosephKK]

petrus bitbyter [email protected] posted to
sci.electronics.design:

----+-------+-----+-5V
| | | +--------------+--2.5V
.-. .-. | | |
| | 10k| | | .-. .-.
| | | | | | | | |
'-'4k7 '-' | | |560k | |56k
| | | '-' '-'
| | |\| | 2k7 |
| +---|-\ | ___ | PIC
SPP | | | |-----+--+-|___|--+--+------
----+-+-----)---|+/ | | I/O
control| | |/| | |
| | LM339 | |
| | | | |
| | | /| | |
| | | /-|--+ |
+-----)-----)---| | | |
| | \+|--)--------+
| | \| | |
| | LM339 | |
.-. | .-. |
| | | | | |
10k| | | | |560k |
'-' | '-' |
| | | |
| | | |
------------+-----+---------+--------+-----
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Modified circuit. This one will work... unless I made another
mistake

petrus bitbyter

It passed all my checks. I would like to see what happens in SPICE.
I will have to cobble it up, tinker and and see some day.

 

[[email protected]]

"petrus bitbyter" <[email protected]> schreef in
bericht









----+-------+-----+-5V
| | | +--------------+--2.5V
.-. .-. | | |
| | 10k| | | .-. .-.
| | | | | | | | |
'-'4k7 '-' | | |560k | |56k
| | | '-' '-'
| | |\| | 2k7 |
| +---|-\ | ___ | PIC
SPP | | | |-----+--+-|___|--+--+------
----+-+-----)---|+/ | | I/O
control| | |/| | |
| | LM339 | |
| | | | |
| | | /| | |
| | | /-|--+ |
+-----)-----)---| | | |
| | \+|--)--------+
| | \| |
| | LM339 |
.-. | .-.
| | | | |
10k| | | | |560k
'-' | '-'
| | |
| | |
------------+-----+---------+--------+-----
GND
created by Andy´s ASCII-Circuit v1.24.140803 Betawww.tech-chat.de

Modified circuit. This one will work... unless I made another mistake

petrus bitbyter- Tekst uit oorspronkelijk bericht niet weergeven -

- Tekst uit oorspronkelijk bericht weergeven -

Oops, I made a mistake. Connected the PIC I/O pin to GND! Which
connectoin should be removed of course. Like I did in the schematic
above.

petrus bitbyter

 

[petrus bitbyter]

petrus bitbyter [email protected] posted to
sci.electronics.design:


It passed all my checks. I would like to see what happens in SPICE.
I will have to cobble it up, tinker and and see some day.

Spiced it using LT1011 as I have no model of the LM339. Seems to work ok.

petrus bitbyter