Parallel port hardware

Jon Slaughter · 2007-10-03T13:31:43+00:00

Does anyone know how the open collector control port in the SPP is +5 | 4.7 kohm | R____|________ TTL input/output | out |/ W---| |\ | GndI can't seem to find anything that shows how the port is read from and I'm trying to understand its behavior when reading based on it. The above is just what I think it probably is but I could be wrong. When reading from the port W must be 0 and then R follows out. But this isn't quite true because R seems to latch W to 1 and I have to write W = 0 to allow R to follow out again.Basically I'm trying to setup an input and output line into a control port pin. I read that I have to use all the pins as either input or output but not mixed? This is probably because I have to reset the pin and I cannot do them individually? If this is the case then I have to use a status port pin to read the line when it is working as an input?... which makes it more complicated.This is where I'm getting most of my info:and this is specifically where I'm having trouble:"An external 4.7k resistor can be used to pull the pin high. I wouldn't use anything lower, just in case you do have an internal pull up resistor, as the external resistor would act in parallel giving effectively, a lower value pull up resistor. When in high impedance state the pin on the Parallel Port is high (+5v). When in this state, your external device can pull the pin low and have the control port change read a different value. This way the 4 pins of the Control Port can be used for bi-directional data transfer. However the Control Port must be set to xxxx0100 to be able to read data, that is all pins to be +5v at the port so that you can pull it down to GND (logic 0)."Not sure why I have to really do all port pins for bi-direction. (Obviously I can't read and write at the same time but I think I can interleave them to get what I want)Any ideas?Thanks,Jon

Oct 03, 2007 27 Replies

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petrus bitbyter 18 years ago

"Jon Slaughter" schreef in bericht news:A7CNi.412$ snipped-for-privacy@nlpi069.nbdc.sbc.com...

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

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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

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Gary Tait 18 years ago

Roger Hamlett wrote in news:xZ1Ni.3317$ snipped-for-privacy@newsfe5-win.ntli.net:

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.

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JosephKK 18 years ago

petrus bitbyter snipped-for-privacy@enditookhccnet.nl posted to sci.electronics.design:

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

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petrus bitbyter 18 years ago

"JosephKK" schreef in bericht news:xRrOi.5167$ snipped-for-privacy@newssvr14.news.prodigy.net...

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

petrus bitbyter

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petrus bitbyter 18 years ago

"petrus bitbyter" schreef in bericht news:470a95a2$0$7076$ snipped-for-privacy@dreader12.news.xs4all.nl...

----+-------+-----+-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

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

petrus bitbyter

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JosephKK 18 years ago

petrus bitbyter snipped-for-privacy@enditookhccnet.nl 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.

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petrus.bitbyter 18 years ago

row

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

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petrus bitbyter 18 years ago

"JosephKK" schreef in bericht news:3f3Pi.2357$ snipped-for-privacy@nlpi069.nbdc.sbc.com...

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

petrus bitbyter

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