Pcf8574

crgwbr

I am trying to write a driver for the PCF8574 I²C 8 bit I/O expander. Since this is the first (non-eeprom) I²C device I've used, I was trying to base it off of this article. But I'm having a few problems translating the BS2p's I2CIN I2COUT commands into something usable for Mike's Basic I2C Driver.

BS2p Constants:

DevType CON %0100 << 4 ' Device type
DevAddr CON %000 << 1 ' address = %000 -> %111
Wr8574 CON DevType | DevAddr ' write to PCF8574
Rd8574 CON Wr8574 | 1 ' read from PCF8574
MixDDR CON %00001111 ' 1 = input, 0 = output

The BS2p I2C command structure is like this:

I2CIN I2Cpin, Rd8574, (MixDDR | ~cntr), [noparse][[/noparse]ioByte]
I2COUT I2Cpin, Wr8574, MixDDR, [noparse][[/noparse]~cntr]

How would this translate into the needed parameters for Mike's driver? I'm thinking that I can do something like this:

VAR
byte Read
byte Write

CON

_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000

DevType %01000000     ' Device type (A0-A2 tied to GND)
MixDDR  %00001111     ' 1 = input, 0 = output

OBJ

I2C : "Basic_I2C_Driver"

PUB Main
'ReadPage(SCL, devSel, addrReg, dataPtr, count) : ackbit
'WritePage(SCL, devSel, addrReg, dataPtr, count) : ackbit

write := %11110000

I2C.ReadPage(0, DevType, MixDDR, @Read, 1)
I2C.WritePage(0, DevType, MixDDR, @Write, 1)

Thanks,
Craig

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Post Edited (crgwbr) : 2/21/2008 9:39:12 PM GMT

QuattroRS4

Craig,
I am using the PCF8574 with a modified version of Mike Greens minimal_i2c_driver .. it works well
currently I am using it for reading inputs only .. with an address of '32' .. A0,A1,A2 all pulled low.

just did a 'search.parallax.com' and found these links .. should get you going

www.rayslogic.com/Propeller/Programming/I2C/i2c.htm
http://forums.parallax.com/showthread.php?p=692852

Regards,
John

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'Necessity is the mother of invention'

deSilva

Well, this may be all you need...
http://forums.parallax.com/showthread.php?p=703283

There is also a piece of code near this thread using the PCF8591 as an example

crgwbr

Thanks John
That just what I was looking for. One more quick question though, I'll be using several PCF8574's on the same bus, therefore they can't all be addressed as %100000 (32). Which 3 bit's do A0, A1, and A2 effect? Does A0,A1,A2 all pulled high create %100111?

Thanks,
Craig

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My system: 1.6 GHz AMD Turion64 X2, 4GB DDR2, 256MB ATI Radeon Graphics card, 15.4" Widescreen HD Screen

I have a duel boot of Ubuntu Linux and Windows Vista. Vista, because it came with the PC, Ubuntu because I like software that works.

"Failure is not an option -- it comes bundled with Windows."

Use The Best...
Linux for Servers
Mac for Graphics
Palm for Mobility
Windows for Solitaire

QuattroRS4

Craig,
Attached please find an image outlining settings and addresses for A2,A1,A0 .. please note that the address range varies in different flavours of the IC .. i.e PCF8574A etc..

Regards,
John

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
'Necessity is the mother of invention'