Using I2C with FullSpeed USB

[Demon]

D'uh, yeah, bits.

I just use I2CREAD for a WORD and get all 16 bits in one shot.

I checked the MicroChip site and they have the MCP23S17 which goes at a maximum of 10MHz in SPI mode. I don't think that's worth the effort to even try.

But I did get another idea; using a 16F628 to read the MCP23016, sets 4 output pins to a binary value (I just need the number of the 1st active pin) and then sets a READY pin. The 18F4550 works on USB until the READY pin is set and then reads the 4 input pins. TADAA!!! Super fast 16 bit parallel exchange between 2 mcus.

I just don't know how the 18F4550 can reset the READY pin though. I never got a full grasp of that concept.

Robert


EDIT: Reviewing my own thread from a while ago:
http://www.picbasic.co.uk/forum/show...ight=busy+line

[mister_e]

mmm, that make me think of few things to try on sunday... i'l do some test with the 4550 and I2C... Anyways i guess that one project i have in head will probably need at least one I2C external device... so i'll hae to mess with I2CREAD/WRITE and/or MSSP anyway.

Your point is valid but need extra hardware... sure workable, but it have to be done without it. The MSSP is the one i mostely suspect workable. SPI is faster than I2C... but MSSP i2C is more fast than PBP I2CREAD/WRITE

mmm...

[Demon]

Steve, I don't have much choice. The SPP feature on the 18F4550 has only 8 bits, I need at least 13.

I wonder if I can do this with discrete components instead of using the MCP23016 and 16F628 to generate a 4 bit combination. I have 13 momentary push-buttons that I have to get to the 18F4550 as fast as possible.

I'm sure there's another way. I'll ask on an electronics forum and see what the gurus there come up with.

Robert

[mister_e]

Sure it have 8 bits... 2 successive read .. well something like stated somewhere in the MCP datasheet. It must exist a quick drwaing of it somewhere in.

if you really want to add stuff, 4 choice spring to mind

use a bigger PIC than the 16F28, then just read the i/o, send it to the 4550 via USART.

Use a keypad decoder like 74c922

Use a single (or more) A/D pin of the 4550 with a multi-step voltage divider... yisssh

Find a multiplexer... time is short now, but it have to exist, i had the 4067 idea... but i'm not sure... i must forget something on this chip.. what? i don't know.

[Demon]

I like the 74C922 keypad decoder, looks simple enough.

Robert


EDIT: Hmmm, looked simple enough until I saw the prices at DigiKey and Mouser. It's 1/2 the price to go with a MCP23016 and PIC 16F628.

[Demon]

Steve, the 4067 multiplexer/demultiplexer is even better and only $2.08CAD at DigiKey.

The only problem is that I don't understand how to get it to go 'backwards'. The A0-3 pins are always referred to as inputs, I need them as outputs. I'm sure there's a way 'cause these are called both names, they must process both ways, no?

Robert


EDIT: "The CD74HC4067 and CD74HCT4067 devices are digitally
controlled analog switches that utilize silicon-gate CMOS
technology to achieve operating speeds similar to LSTTL,
with the low power consumption of standard CMOS
integrated circuits.
These analog multiplexers/demultiplexers control analog
voltages that may vary across the voltage supply range.
They are bidirectional switches thus allowing any analog
input to be used as an output and vice-versa. The switches
have low “on” resistance and low “off” leakages. In addition,
these devices have an enable control which when high will
disable all switches to their “off” state."

It should work.

[Demon]

74HC148 encoder here:
http://www.st.com/stonline/books/pdf/docs/1903.pdf

Page 7 has a schematic to cascade 2 chips with 16 inputs to 4 outputs. $0.31CAD when I buy 100 at DigiKey and I only need an AND and NOT gates to go along with them.

Robert