AT89C51ED2-RDTIM datasheet(119/137 Pages) ATMEL

119 / 137 page

119

AT89C51RD2/ED2

4235E–8051–04/04

AC Parameters

Explanation of the AC

Symbols

Each timing symbol has 5 characters. The first character is always a “T” (stands for

time). The other characters, depending on their positions, stand for the name of a signal

or the logical status of that signal. The following is a list of all the characters and what

they stand for.

Example:TAVLL = Time for Address Valid to ALE Low.

TLLPL = Time for ALE Low to PSEN Low.

(Load Capacitance for port 0, ALE and PSEN = 100 pF; Load Capacitance for all other

outputs = 80 pF.)

Table 77 Table 80, and Table 83 give the description of each AC symbols.

Table 78, Table 79, Table 81 and Table 84 gives the range for each AC parameter.

Table 78, Table 79 and Table 85 give the frequency derating formula of the AC parame-

ter for each speed range description. To calculate each AC symbols. take the x value in

the correponding column (-M) and use this value in the formula.

Example: T

LLIU for -M and 20 MHz, Standard clock.

x = 35 ns

T 50 ns

CCIV = 4T - x = 165 ns

External Program Memory

Characteristics

Table 77. Symbol Description

Symbol

Parameter

Oscillator clock period

TLHLL

ALE pulse width

TAVLL

Address Valid to ALE

TLLAX

Address Hold After ALE

TLLIV

ALE to Valid Instruction In

TLLPL

ALE to PSEN

TPLPH

PSEN Pulse Width

TPLIV

PSEN to Valid Instruction In

TPXIX

Input Instruction Hold After PSEN

TPXIZ

Input Instruction Float After PSEN

TAVIV

Address to Valid Instruction In

TPLAZ

PSEN Low to Address Float

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