EM78815
8-Bit Microcontroller
Max. of 2M Byte Expanded ROM
(FLASH ROM)
Expanded Data ROM Start Address
RF Page 2 RF Page 1
64K Program ROM
Unused
IOCB
B7 B7
128K word Program ROM
(Page 0 ~ Page 127)
B0 B7
B0
X
0
0
0
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
0
ROM
Address 17
ROM
Address 0
ROM
Address 9
256K byte
Data ROM
Expanded Data ROM
EM78815
(EXSEL pin pull high)
Fig. 4b EXSEL = 1, Only External Program is Used
Setting the expanded Data ROM’s Starting Address
The EM78815 supports a maximum of 2M Bytes expanding data memory, but user
must fix the start address of the external program at 0x00000 and set the start
address of the expanded Data ROM since the program ROM size is adjustable. In
this way, the MCU will get data from the external memory if the data ROM is over
256K.
The instruction width is 13 bits and the data bus for external memory is 8 bits, so an
instruction will capture two address sizes and the LSB address of the start address at
the external ROM will be 0. Besides, the EM78815 only supports a max of 128K
program, so the start address of the Data ROM will be smaller than 256K+2 and A20,
A19 and A18 will also be 0. User must set the expanded start address of the Data
ROM at A17~A1 to IOCB Page 2, Bit 7, RF Page 3 and RF Page 2.
10 •
Product Specification (V2.4) 02.17.2006
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
