
111
AT89C51RB2/RC2
4180E–8051–10/06
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.)
eter for each speed range description. To calculate each AC symbols, take the x value
in the correponding column (-M or -L) and use this value in the formula.
Example: T
LLIU for -M and 20 MHz, Standard clock.
x = 35 ns
T 50 ns
T
CCIV = 4T - x = 165 ns
External Program Memory
Characteristics
Table 75. Symbol Description
Symbol
Parameter
T
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