SM89516B
8-Bit Micro-controller
64KB Flash
& 1KB RAM embedded
A[9:0]
DPTR
Bank 2 (256B)
{RAMS1,RAMS0,@Ri}
MUX
{DBANK[3:0],direct
address}
768
Bytes
Bank 1 (256B)
READ
Bank 0 (256B)
WRITE
On-chip 768B expanded RAM
OME
MOVX @Ri instrcution
SEL
MOVX @DPTR instrcution
Control Logic
DPTR
Chip selection of on-chip expanded RAM
{RAMS1,RAMS0}
DBANK[7]
Fig. 3-3: Access on-chip expanded RAM scheme
Method 2 : By direct addressing MOV instruction
The 768B on-chip expanded data RAM and 256B scratchpad RAM is combined together to form a 1KB memory
space. This 1KB space is logically partitioned into 16 pieces of 64B RAM bank. This 1KB space can be accessed
through a single-addressing-type MOV instruction with bank-switch technique. In this technique, the 64B address
range $40 - $7F in direct addressing MOV instruction is used as mapping window and is concatenated with bit3 –
bit0 in DBANK register to address up to 1KB memory space.
While accessed by direct addressing MOV instruction, the 768B expanded RAM is address-offset by 256 bytes
upward and concatenates with scratchpad RAM to form a 1KB memory space. Hence 768B expanded RAM
occupies address space from $100 to $2FF and 256B scratchpad RAM is located from $000 to $0FF.
With the address mapping window and bank switching scheme, user can use single type MOV instruction to access
entire 1K bytes on-chip data memory space. For example, users can have following assembly codes to write data
0x30 into expanded 768B data ram address $101 :
MOV DBANK,#88H
MOV A,#30H
MOV 41H, A
Specifications subject to change without notice contact your sales representatives for the most recent information.
ISSFD-M087
Ver A SM89516B 3/7/2014
- 20 -
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
