Department of Computer Scien

ce and Information Engineering

National Cheng Kung University

HANEL

INTERFACING EXTERNAL

ROM

On-Chip and Off-Chip Code

ROM

‰In an 8751 system we could use on-chip ROM for boot code and an external ROM will contain the user’s program

¾We still have EA = V

, cc

ƒUpon reset 8051 executes the on-chip program first, then ƒWhen it reaches the end of the on-chip ROM, it switches to external ROM for rest of program8031/51EA = GNDOffChip

0000 ~FFFF

~

(^8051) EA = Vcc
(^0000) FFFF

OffChip~

~

On-chip

0FFF^1000

FFFF

(^8052) EA = Vcc
0000

OffChip~

~

On-chip

1FFF^2000

On-chip and Off-chip Program Code Access