80C451 datasheet(13/22 Pages) PHILIPS

13 / 22 page

Philips Semiconductors

Product specification

80C451/83C451/87C451

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, expanded I/O

1998 May 01

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 2. External Program Memory Read Cycle

tLLAX

ALE

PSEN

PORT 0

PORT 2

A0–A7

FROM RI OR DPL

DATA IN

A0–A7 FROM PCL

INSTR IN

P2.0–P2.7 OR A8–A15 FROM DPH

A0–A15 FROM PCH

tWHLH

tLLDV

tLLWL

tRLRH

tRLAZ

tAVLL

tRHDX

tRHDZ

tAVWL

tAVDV

tRLDV

SU00007

Figure 3. External Data Memory Read Cycle

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