8051 packaging, does it matter?

[CuentaChocula]

I've got a few Atmel AT89C55 chips. Some are DIP40 (AT89C55WD) and some are PLCC44 (AT89C55). If I wire up a PLCC socket to a DIP Socket with the corresponding pins from the PLCC to the right pins on the DIP, will it program ok and work the same as the DIP chips? I was told by someone that it wouldn't work, but I don't see why not. Thanks.

 

[ericgibbs]

hi,
Although the PLCC version has 44 pins compared to the DIP package, 4 of
the PLCC pins are N/C.

Provided you connect them for pin function to the same pin function on the
other PIC pin. Example P1.5 to P1.5. it will be OK.

I mean do not go pin 1 to pin 1 and so on.

Ask again if my explanation is not clear.

Regards
EricG

 

[sci-3d]

If the pins are the same, this would be ok.

 

[CuentaChocula]

Thanks Eric and Sci,

Yes, I realize that pin #x on plcc isn't necessarily the same pin # on dip and that there are a few n/c pins on the plcc package. I have the datasheets on both chips so I can map each pin based on what it's name / function is. So, that will work? Cool.

 

[dknguyen]

Yeah, it'd work because semiconductor companies are cheap. WHy would they spend money to make different masks for the same silicon die just because it's in a different package? They just use the same silicon die and "can" it differently, so all pins are identical across different packages and unused pins are just N/C.

 

[Sceadwian]

Not all. I've seen several AVR's that have extra pins on PLCC or MLF packages that don't exist on their dip counter parts. Mostly it's Xtal or auxiliary functions like ADC and VREF signals that would otherwise share I/O pins moved to dedicated pins to free up some general purpose I/O this is easy enough to do with OTP fuses.

 

[ashad]

the packaging is depend upon the number of I/O Function of the Chip and the working environment of the chip