Driving LCD with I2C I/O expander (PCF8574)
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Posts: 46,084
Does anyone know if it is possible to drive LCD (in 4 bit mode) via
PCF8574 (8 bit i2c i/o expander) so that PCF8574 drives 4 bits for
data, RS, R/W and E?
I've been successful in using PCF8574 to drive the 4 bits for data,
RS and R/W, but not E. I have to use a Stamp port to drive the E
signal.
Has anyone some knowledge if this is even possible?
I've read that internal structure of the PCF8574 is a shift register.
I think this may be the problem (i.e. I cannot obtain a clean High to
Low signal for E via PCF8574).
If anyone has some info., I would really appreciate it.
Happy stamping to y'all...
PCF8574 (8 bit i2c i/o expander) so that PCF8574 drives 4 bits for
data, RS, R/W and E?
I've been successful in using PCF8574 to drive the 4 bits for data,
RS and R/W, but not E. I have to use a Stamp port to drive the E
signal.
Has anyone some knowledge if this is even possible?
I've read that internal structure of the PCF8574 is a shift register.
I think this may be the problem (i.e. I cannot obtain a clean High to
Low signal for E via PCF8574).
If anyone has some info., I would really appreciate it.
Happy stamping to y'all...
Comments
sinking power (enough for logic at least) but has virtually no sourcing
capability (25ma sink but only 300uA source per pin if I remember
correctly). Might you be overloading its output capability and dropping
voltage below what the LCD can read?
If this is the problem (and it may well not be!) the 74HC595 might be a good
replacement. More I/O pins needed on the stamp. The other possibility would
be to feed the 8574 outputs to a transciever chip like the 74xx244 or 245
and let them source the LCD.
I'm a newb shooting in the dark though so don't take my word as gospel.
My 'lectronic Newb site http://members.shaw.ca/pmeloy/
Original Message
From: <basicstampede@y...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, February 26, 2003 1:28 PM
Subject: [noparse][[/noparse]basicstamps] Driving LCD with I2C I/O expander (PCF8574)
> Does anyone know if it is possible to drive LCD (in 4 bit mode) via
> PCF8574 (8 bit i2c i/o expander) so that PCF8574 drives 4 bits for
> data, RS, R/W and E?
>
> I've been successful in using PCF8574 to drive the 4 bits for data,
> RS and R/W, but not E. I have to use a Stamp port to drive the E
> signal.
>
> Has anyone some knowledge if this is even possible?
> I've read that internal structure of the PCF8574 is a shift register.
> I think this may be the problem (i.e. I cannot obtain a clean High to
> Low signal for E via PCF8574).
>
> If anyone has some info., I would really appreciate it.
>
> Happy stamping to y'all...
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
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>
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>
>
other types) that they sink well, but don't source well.
ARRL Handbook, 2002 (by the way, these are great sources of general
electronic information and sometimes available at the local library),
74HC series Max clock frequency 30 MHz, output sink 8 mA. It doesn't
list the source current, but I would guess it to be less than 0.5 mA.
Original Message
From: Pat M [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=us-oUePKtC9EqpWyUkZD2ViZNLqqwLPvYqNonKXcEA8IpvQVAojZCNrLRq5jUshOUxtNDg]pmeloy@s...[/url
Sent: Wednesday, February 26, 2003 6:05 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] Driving LCD with I2C I/O expander (PCF8574)
Dont know if this has anything to do with it but, the PCF8574 is fine
for sinking power (enough for logic at least) but has virtually no
sourcing capability (25ma sink but only 300uA source per pin if I
remember correctly). Might you be overloading its output capability and
dropping voltage below what the LCD can read?
If this is the problem (and it may well not be!) the 74HC595 might be a
good replacement. More I/O pins needed on the stamp. The other
possibility would be to feed the 8574 outputs to a transciever chip like
the 74xx244 or 245 and let them source the LCD.
I'm a newb shooting in the dark though so don't take my word as gospel.
My 'lectronic Newb site http://members.shaw.ca/pmeloy/
Original Message
From: <basicstampede@y...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, February 26, 2003 1:28 PM
Subject: [noparse][[/noparse]basicstamps] Driving LCD with I2C I/O expander (PCF8574)
> Does anyone know if it is possible to drive LCD (in 4 bit mode) via
> PCF8574 (8 bit i2c i/o expander) so that PCF8574 drives 4 bits for
> data, RS, R/W and E?
>
> I've been successful in using PCF8574 to drive the 4 bits for data, RS
> and R/W, but not E. I have to use a Stamp port to drive the E signal.
>
> Has anyone some knowledge if this is even possible?
> I've read that internal structure of the PCF8574 is a shift register.
> I think this may be the problem (i.e. I cannot obtain a clean High to
> Low signal for E via PCF8574).
>
> If anyone has some info., I would really appreciate it.
>
> Happy stamping to y'all...
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject
> and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject
and Body of the message will be ignored.
Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/