Philips Semiconductors
Product data
P87C51RA2/RB2/RC2/RD2
80C51 8-bit microcontroller family 8KB/16KB/32KB/64KB OTP
with 512B/1KB RAM, low voltage (2.7 to 5.5 V), low power, high
speed (30/33 MHz)
2003 Jan 24
50
EXPLANATION OF THE AC SYMBOLS
Each timing symbol has five characters. The first character is always
‘t’ (= time). The other characters, depending on their positions,
indicate the name of a signal or the logical status of that signal. The
designations are:
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 – Float
Examples: tAVLL = Time for address valid to ALE low.
tLLPL =Time for ALE low to PSEN low.
tPXIZ
ALE
PSEN
PORT 0
PORT 2
A0–A15
A8–A15
A0–A7
tAVLL
tPXIX
tLLAX
INSTR IN
tLHLL
tPLPH
tLLIV
tPLAZ
tLLPL
tAVIV
SU00006
tPLIV
Figure 34. External Program Memory Read Cycle
ALE
PSEN
PORT 0
PORT 2
RD
A0–A7
FROM RI OR DPL
DATA IN
A0–A7 FROM PCL
INSTR IN
P2.0–P2.7 OR A8–A15 FROM DPF
A0–A15 FROM PCH
tWHLH
tLLDV
tLLWL
tRLRH
tLLAX
tRLAZ
tAVLL
tRHDX
tRHDZ
tAVWL
tAVDV
tRLDV
SU00025
Figure 35. External Data Memory Read Cycle