Is it possible to reprogram this chip?

[ericgibbs]

It looks like your coding a shift register D0 D1 D3 D4 you set all that for input or output don't want none of that LOL

**broken link removed**

hi Burt,
The 8255A was commonly used as a port expander, PortA and PortB could be set as bi directional and PortC could be Bit selected.

The IC performed well for the era and the applications it was designed for..

 

[Pommie]

G'day Mike, Prosperous 2011...

I have used the 8255A in many designs and products with virtually no problems.

Its unlike you to use descriptors like 'pretty horrid' , usually you present a logical argument.

I would be interested to know the problems you encountered with the 8255A.

Regards

G'day Eric,

Yes, you are correct, "pretty horrid" isn't the most logical argument. However, I seem to remember having to select different modes and nothing was straight forward and had to be achieved in some convoluted way. Maybe it's just my fading memory but I do recall finding the 6522 very easy to use in comparison to the 8255.

Hope you too have a happy and prosperous new year.

Mike.

 

[Mike - K8LH]

I used a 6522 VIA chip on an Apple ][ plug-in board a long time ago. It worked very well...

 

[Nigel Goodwin]

I used a 6522 VIA chip on an Apple ][ plug-in board a long time ago. It worked very well...

Yes, the 6522 was a far superior device, which makes the 8255 look so bad.

Neither of them are port expanders of course, but are memory mapped PIA's for micro-processors.

 

[ericgibbs]

Neither of them are port expanders of course, but are memory mapped PIA's for micro-processors.

Happy 2011,

Sorry to disagree, the 8255A IMO makes a suitable port expander, for 8 data lines and 5 control lines from a MCU it can provide an additional 14 I/O pins.

By any definition I would call that port expansion....

EDIT:
Corrected control line count from 3 to 5...

 

[Pommie]

Happy 2011,

Sorry to disagree, the 8255A IMO makes a suitable port expander, for 8 data lines and 3 control lines from a MCU it can provide an additional 16 I/O pins.

By any definition I would call that port expansion....

Hi Eric,

Happy new year.

I think you forgot the 2 address lines.

Mike.

 

[ericgibbs]

Hi Eric,

Happy new year.

I think you forgot the 2 address lines.

Mike.

Happy New Year Mike,
Its quite a while since I last used the device, you are correct.

Even so, for Nigel to dismiss my comment about it being used as a port expander is a little over the top.

I have used literally hundreds of the damned things in many applications, including the provision of extra I/O pins.

 

[Pommie]

Hi Eric,

The last time I used an 8255 was in the mid 80s and I think it was in either an Amstrad CPC or a Tatung Einstien.

Mike.

 

[ericgibbs]

Hi Eric,

The last time I used an 8255 was in the mid 80s and I think it was in either an Amstrad CPC or a Tatung Einstien.

Mike.

hi,
I switched over to the Z84C90 in the late 80's early 90's.

I have lots of them still in stock.!