
143
AT89C51ID2
4289C–8051–11/05
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:T
AVLL = Time for Address Valid to ALE Low.
T
LLPL = 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.)
parameter 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 98. Symbol Description
Symbol
Parameter
T
Oscillator clock period
T
LHLL
ALE pulse width
T
AVLL
Address Valid to ALE
T
LLAX
Address Hold After ALE
T
LLIV
ALE to Valid Instruction In
T
LLPL
ALE to PSEN
T
PLPH
PSEN Pulse Width
T
PLIV
PSEN to Valid Instruction In
T
PXIX
Input Instruction Hold After PSEN
T
PXIZ
Input Instruction Float After PSEN
T
AVIV
Address to Valid Instruction In
T
PLAZ
PSEN Low to Address Float