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
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...
Output can never be greater than VCC.
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.- snipped-for-privacy@w5g2000prd.googlegroups.com...
ys this happens if the capacitance on the pin is more than
oading on the I/O. The I/O pin has a sort of latch
n "tri-state" mode, which it is after the reset. But after
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 =3D 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
Yes, unless they're listed as "TTL Compatible", which the D82C55AC-2 is.
Hope This Helps! Rich
How much power supply current is it drawing? ;-)
Hint: It's not all that hard to re-mark old ICs.
Best regards, Spehro Pefhany
Sounds like you got 3.3 V parts when you thought you ordered 5 V parts.
Have something to add? Share your thoughts — no account required.
Ask the community — no account required