Interconnected chips and pin settings

Noob playing with a 16f887 and a umFPU math coprocessor.

After frying a couple of umFPUs I've realized that I need to be setting the TRISx and PORTx settings (see, noob). I think that after a number of power-on resets one of the Pic pins went high and nearly melted the breadboard under the umFPU and cooked the umFPU chip (but Pic was OK).

I've now set the pins to inputs and set them low but am hesitant to potentially blow yet another chip. Is this the proper setting for pins connected to other chips? Is there any other option?

Thanks.

I think it was pin C4 or C5 that went high.


'-------------------- uM-FPU pin definitions ----------------------------------
FpuClk var PORTC.3 ' SPI SCLK (uM-FPU SCLK)
FpuIn var PORTC.4 ' SPI MISO (uM-FPU SOUT)
FpuOut var PORTC.5 ' SPI MOSI (uM-FPU SIN)

What voltage are you running the PIC at and what is the max voltage of the other chip? The max voltage it can handle?

I am running both the 16f887 and umFPU at 3.3V.

umFPU can run at up to 5V.

can you not put resisters between the pic and the mathco? that should stop the mathcpu from grounding sending a pic output line to ground and poping the chip...

But yes, the startup of the chip needs to send all outputs low and then set the relivant lines to inputs right at the beginning...

So...

Code:

---

TRISE = %00000111
TRISD = %00000000
TRISC = %00000000
TRISB = %00000000
TRISA = %11111111
PORTA = 0
PORTB = 0
PORTC = 0
PORTD = 0
PORTE = 0

---

Setting TRIS to 1 makes that bit an input...
the PORT commands makes all the ports low...

I hope that helps

Thanks Comwarrior, I think that resistors between the two processors is what was needed.