Ever wonder why?

[cncmachineguy]

There have been many many things in my life that I had to wonder - why? But one that keeps coming back is no matter how big the device is, it is still 1 or 2 pins short? Why? Currently I am using the biggest device I can find in the 8 bit world 100 pins. I don't want the latency of port expanders so I am using some buffers to double up on some inputs. Yet still I found myself looking for a way to simply add an led.

I resolved the lack of I/O, but just have to wonder -WHY?

[Charles Linquis]

I have the same issue. I solve it most of the time by having an expansion header on most of my boards. It brings up power, the second I2C port/SPI port, the second TX/RX and PORTB.1, PORTB.6, PORTB.7 and MCLR.

I use one 7 pin connector to connect my ICD3. PGC and PGD from each of the chips goes through a 1K resistor before going to the programming header.
There are 2 (sometimes 3) MCLR connections on the 7 pin header (one for each chip), and a multi-position switch on the ICD3 cable switches one line between the MCLR of chip 1 and the MCLR of chip 2 (and possibly, chip 3).

One connection can program all the chips sequentially (of course, you have to manually toggle the MCLR switch).

I have boards that have 3 8723's! Plenty of pins!

[Jerson]

My answer : Guess the chip manufacturers have conspired to get us for the last pin )

[Charles Linquis]

Bert,I thought I was about the only one here using so many pins. This makes me wonder what you are up to. What are you building that takes so much I/O?

[rsocor01]

This makes me wonder what you are up to. What are you building that takes so much I/O?

Yes, what are you building? Some kind of space craft? PICs with 100 pins have from 70 to 85 I/O pins, more than enough for most projects.

[cncmachineguy]

@ Jerson, I agree completly!!

Short answer - machine controller

The project is an interface between PC parallel port and up to 10 axis of stepper/servos with 2 inputs per axis for limit/home switches. Also a couple of relays for some high power stuff.

So the parallel port itself uses 12 pins, then each axis is 5 pins. so thats 62 right there. I have run out so I must have forgot some things.
It will use 2 50 pin connectors to plug into 2 5 axis cards and carry all the needed stuff to them. Full digital setup for the stepper drives on these cards.

[kellyseye]

That's why some clever so and so invented 'multiplexing'.....

[mister_e]

Agree, but sometimes, multiplexing is not a solution while I/O expander are.

Conspiracy I tell you