AT89C51RB2/RC2
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.
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.)
Table 75 Table 78, and Table 80 give the description of each AC symbols.
Table 77, Table 79 and Table 81 give the AC parameterfor each range.
Table 76, Table 77 and Table 82 gives the frequency derating formula of the AC param-
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: TLLIU for -M and 20 MHz, Standard clock.
x = 35 ns
T 50 ns
TCCIV = 4T - x = 165 ns
External Program Memory
Characteristics
Table 75. Symbol Description
Symbol
T
Parameter
Oscillator clock period
ALE pulse width
TLHLL
TAVLL
TLLAX
TLLIV
TLLPL
TPLPH
TPLIV
TPXIX
TPXIZ
TAVIV
TPLAZ
Address Valid to ALE
Address Hold after ALE
ALE to Valid Instruction In
ALE to PSEN
PSEN Pulse Width
PSEN to Valid Instruction In
Input Instruction Hold after PSEN
Input Instruction Float after PSEN
Address to Valid Instruction In
PSEN Low to Address Float
111
4180E–8051–10/06
ATMEL [ ATMEL ]
