EM78815
8-Bit Microcontroller
6.8 Expand Program/Data ROM Interface
Pin
EXD0 ~ EXD7
/RD
I/O
I/O
O
Description
Expand Program/Data memory Data Bus
Expand Program/Data memory Read request output
Expand Program/Data memory Write request output
Expand Program/Data memory CS request output
Expand Program/Data memory Address Bus
0/1 Æ Internal 64K Program ROM used/unused
/WR
O
/CS
O
EX0~EXA20
EXSEL
O
I
EXSEL pin : 0/1 → On-chip program ROM used/unused switch.
The EM78815 supports a max. of 128K Program. User can support program for both
64K EM78815 on-chip ROM and 64K expanded ROM. User can also ignore the 64K
EM78815 on-chip ROM and support all programs for an external 128K ROM. Using
this function, user can easily upgrade programs or download new functions.
The EM78815 provides Data ROM expanded function. When user access data of
which address is over 256K, the external ROM will be loaded. User must set the
expanded start address of the Data ROM to RF Page 1, Page 2 and IOCB Page 1. A
diagram of the expanded function is shown below.
Max. of 2M Byte Expanded ROM
(FLASH ROM)
Expanded Data ROM Start Address
64K Program ROM
(Page 0 ~ Page 63)
RF Page 2
RF Page 1
IOCB
B7B7
64K word Program ROM
(Page 64 ~ Page127
B0 B7
X
B0
0 0
0
X X X X
X
X X X X
X
X
X
X
X
X
X 0
ROM
Address 0
ROM
Address 17
ROM
Address 9
256K Byte
Data ROM
Expanded Data ROM
EM78815
(EXSEL pin go low)
Fig. 4a EXSEL = 0, Both Internal and External Programs are Used
Product Specification (V2.4) 08.01.2004
(This specification is subject to change without further notice)
9
ELAN [ ELAN MICROELECTRONICS CORP ]
