D82C55AC-2

[aleksa]

I've bought 10 pcs of "82C55" through mail, and received D82C55AC-2.

The problem is that the output high voltage of any pin is not 5V, but
3.8V.

Nothing is connected to the port pins, VCC is 4.85V.

Am I wrong thinking that CMOS chips should have far more than 3.8V on
output pins?

Thanks

 

[Don McKenzie]

I've bought 10 pcs of "82C55" through mail, and received D82C55AC-2.

The problem is that the output high voltage of any pin is not 5V, but
3.8V.

Nothing is connected to the port pins, VCC is 4.85V.

Am I wrong thinking that CMOS chips should have far more than 3.8V on
output pins?

Thanks

google a data sheet. will be there.

Cheers Don...


--
Don McKenzie

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[linnix]

I've bought 10 pcs of "82C55" through mail, and received D82C55AC-2.

The problem is that the output high voltage of any pin is not 5V, but
3.8V.

Nothing is connected to the port pins, VCC is 4.85V.

Output can never be greater than VCC.

 

[aleksa]

The I/O pins can be in between state after a reset. The Intel datasheet says this happens if the capacitance on the pin is more than
20 pf, but I have seen this happen with chips that had little capacitive loading on the I/O. The I/O pin has a sort of latch
function to hold the previous state of the output pin when the output is in "tri-state" mode, which it is after the reset. But after
a reset the latch function is in the linear range and can get stuck in an in-between state.

The intel pdf on 82C55 says that the
Output High Voltage is minimum 3.0V with 2.5mA load,
and VCC-0.4V with 100uA load.

Since there is nothing connected to the pins,
it should be minimum 4.85-0.4 = 4.45V, not 3.8V.

If I try the D71055C, the output pin is exactly VCC.

(both D82C55AC and D71055C are from NEC)

The chip is initialized after the reset,
all ports are in output mode,
and all ports are written with 0FFh.

P.S.
It is close to 2am, I'm going to bed

 

[Rich Grise]

I've bought 10 pcs of "82C55" through mail, and received D82C55AC-2.

The problem is that the output high voltage of any pin is not 5V, but
3.8V.

Nothing is connected to the port pins, VCC is 4.85V.

Am I wrong thinking that CMOS chips should have far more than 3.8V on
output pins?

Yes, unless they're listed as "TTL Compatible", which the D82C55AC-2 is.

Hope This Helps!
Rich

 

[Eeyore]

I've bought 10 pcs of "82C55" through mail, and received D82C55AC-2.

The problem is that the output high voltage of any pin is not 5V, but
3.8V.

Nothing is connected to the port pins, VCC is 4.85V.

Am I wrong thinking that CMOS chips should have far more than 3.8V on
output pins?

That's an Intel design and their early 'CMOS' processors and peripherals
were 'CHMOS' rather than true CMOS IIRC.

One consequence was the output high voltage was indeed as you mention.
Sounds quite normal to me. What on earth are you using them for anyway ?

Graham

 

[JosephKK]

I've bought 10 pcs of "82C55" through mail, and received D82C55AC-2.

The problem is that the output high voltage of any pin is not 5V, but
3.8V.

Nothing is connected to the port pins, VCC is 4.85V.

Am I wrong thinking that CMOS chips should have far more than 3.8V on
output pins?

Thanks

Sounds like you got 3.3 V parts when you thought you ordered 5 V
parts.

 

[Eeyore]

Sounds like you got 3.3 V parts when you thought you ordered 5 V
parts.

AFAIK there never was a '3.3V' 8255. It's an ancient I/O expander IIRC.

Graham

 

[Rich Grise]

AFAIK there never was a '3.3V' 8255. It's an ancient I/O expander IIRC.

And the one cited by the OP is listed as TTL compatible, so Voh over
2.4V is within spec. IOW, it's operating perfectly normally, For an 8255.

But I can't imagine what would possess anyone to specify one - it's a
programming nightmare. OP'd be better off to make an I/O thing with
some kind of FPGA or CPLD or even an 8748 - I've used one of them for
a smart peripheral interface (actually, a FIFO, because at the time,
designing and building a little 8748 PCB was cheaper than a raw FIFO
chip.)

Cheers!
Rich

 

[Eeyore]

And the one cited by the OP is listed as TTL compatible, so Voh over
2.4V is within spec. IOW, it's operating perfectly normally, For an 8255.

That's what I reckon too.

But I can't imagine what would possess anyone to specify one - it's a
programming nightmare. OP'd be better off to make an I/O thing with
some kind of FPGA or CPLD or even an 8748 - I've used one of them for
a smart peripheral interface (actually, a FIFO, because at the time,
designing and building a little 8748 PCB was cheaper than a raw FIFO
chip.)

Not sure even why you'd use an 8748. 8xC51s are so cheap these days (and do
have genuine CMOS swings) and are very widely available. Who still makes the
8748 ?

Graham