
P89V52X2_3
NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 03 — 4 May 2009
46 of 57
NXP Semiconductors
P89V52X2
80C51 with 256 B RAM, 192 B data EEPROM
9.1 Explanation of symbols
Each timing symbol has 5 characters. The rst 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.
A — Address
C — Clock
D — Input data
H — Logic level HIGH
I — Instruction (program memory contents)
L — Logic level LOW or ALE
P — PSEN
Q — Output data
R — RD signal
T — Time
V — Valid
W — WR signal
X — No longer a valid logic level
Z — High impedance (Float)
Example:
tAVLL = Address valid to ALE LOW time
tLLPL = ALE LOW to PSEN LOW time
Fig 21. External program memory read cycle
002aaa548
port 2
PSEN
ALE
A0 to A7
tLLAX
tPLAZ
tPXIZ
tLLPL
tAVIV
tAVLL
tLLIV
tPLIV
tPLPH
INSTR IN
A8 to A15
A0 to A7
port 0
tPXIX
tPXAV
tLHLL