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Electrical characteristics

AN2021

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5.2

AC characteristics at 40 MHz

As the two devices have a different technology, the I/Os also present some differences in the

AC behavior. The tables below (Table 20 and Table 21) list all the timing differences. Please

check carefully your design for possible impact.

5.2.1

External memory bus timings

Note that for CPU clock frequencies above 40 MHz, some numbers in the timing formulas

become zero or negative, that in most of the cases is not acceptable or not meaningful at all.

In these cases, it is necessary to reduce the speed of the bus setting properly tA (ALE

extension), tC (Memory Cycle Time wait-states) and tF (Memory tri-state time).

VOLCC

Output low

voltage

–

Port0, Port1, Port4,

ALE, RD, WR, BHE,

CLKOUT, RSTOUT

0.45 / IOL =

2.4mA

–

Port6, ALE,

CLKOUT, WR,

READY, BHE, RD,

RSTOUT, RSTIN

0.4 / IOL = 8mA

0.05 / IOL = 1mA

VOL1CC

Output low

voltage (all

other)

–0.45 / IOL =

2.4mA

–0.4 / IOL =4mA

0.05 /

IOL =0.5mA

VOHCC

Output high

voltage

0.9VDD /IOH =

-0.5mA

2.4 / IOH = -2.4mA

–

Port0, Port1,

Port4, RD, ALE,

BHE, WR,

CLKOUT,

RSTOUT

VDD - 0.8 / IOH =

-8mA

VDD - 0.08/ IOH =

-1mA

–

Port6, ALE,

CLKOUT, WR,

READY, BHE,

RD, RSTOUT,

RSTIN

VOH1CC

Output high

voltage (all

other)

0.9VDD /IOH =

-0.25mA

2.4 / IOH = -1.6mA

–

VDD - 0.8 / IOH =

-4mA

VDD -0.08/IOH =

-0.5mA

–V

IOZ1CC

Input leakage

current (Port 5)

–

±0.5

–

±0.2

µA

IOZ2CC

Input leakage

current (all other

inputs)

–±1

–

±0.5

µA

Table 19.

DC characteristics (continued)

Symbol

Parameter

ST10F269 Limit values

ST10F272 Limit values

Unit

Min

Max

Min

Max

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