The Microcontroller Idea Book - Jan Axelson's Lakeview Research

The 82C55 also has CMOS-compatible outputs, which means that they can drive either
LSTTL or CMOS inputs. When driving CMOS inputs, the NMOS 8255’s outputs should
have pull-up resistors to ensure that high outputs are at least 3.5 volts.
A third advantage to the 82C55 is greater current-sourcing ability, which can be important
if you want to directly drive a transistor or source more than a fraction of a milliampere.
Intel’s 82C55 can source 2.5 milliamperes at 3 volts, compared to just 0.4 milliamperes at
2.4 volts for the 8255. However, NEC’s CMOS 71055 has the same current-sourcing ability
as the NMOS 8255, so it depends on the manufacturer. All can sink 2.5 milliamperes at 0.45
volts. The 74LS374 latch (U14) has greater output drive ability than any of the 8255s.
Speed Ratings
Inputs and Outputs
The 8255 is also available with different speed ratings, including 3 Mhz and 5 Mhz. The
5-Mhz part is sometimes called the 8255-5. From the ratings, it may seem that the 8255 is
too slow to interface to a 12-Mhz 8052-BASIC. But what does the speed rating actually
refer to? Since the 8255 was developed for the 8085, I suspect that it refers to the maximum
Figure 6-5. Pinout of the 8255 Programmable Peripheral Interface.
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