FlashFlex MCU
SST89E516RD2 / SST89E516RD
SST89V516RD2 / SST89V516RD
Data Sheet
3.2.1 Reset Configuration of Program Memory
Block Switching
3.4 Expanded Data RAM Addressing
The SST89E/V516RDx have the capability of 1 KByte
RAM. See Figure 3-2.
Program memory block switching is initialized after reset
according to the state of the Start-up Configuration bit SC0.
The SC0 bit is programmed via an external host mode
command or an IAP Mode command. See Table 4-3.
The device has four sections of internal data memory:
1. The lower 128 Bytes of RAM (00H to 7FH) are
directly and indirectly addressable.
Once out of reset, the SFCF[0] bit can be changed dynam-
ically by the program for desired effects. Changing SFCF[0]
will not change the SC0 bit.
2. The higher 128 Bytes of RAM (80H to FFH) are
indirectly addressable.
Caution must be taken when dynamically changing the
SFCF[0] bit. Since this will cause different physical memory
to be mapped to the logical program address space. The
user must avoid executing block switching instructions
within the address range 0000H to 1FFFH.
3. The special function registers (80H to FFH) are
directly addressable only.
4. The expanded RAM of 768 Bytes (00H to 2FFH) is
indirectly addressable by the move external
instruction (MOVX) and clearing the EXTRAM bit.
(See “Auxiliary Register (AUXR)” in Section 3.6,
“Special Function Registers”)
TABLE
3-2: SFCF Values Under Different Reset
Conditions
Since the upper 128 Bytes occupy the same addresses as
the SFRs, the RAM must be accessed indirectly. The RAM
and SFRs space are physically separate even though they
have the same addresses.
State of SFCF[1:0] after:
Power-on
or
WDT Reset
or
External
Reset
Brown-out
Reset
Software
Reset
SC01
When instructions access addresses in the upper 128
Bytes (above 7FH), the MCU determines whether to
access the SFRs or RAM by the type of instruction given. If
it is indirect, then RAM is accessed. If it is direct, then an
SFR is accessed. See the examples below.
U (1)
00
(default)
x0
10
P (0)
01
x1
11
T3-2.0 1273
1. P = Programmed (Bit logic state = 0),
U = Unprogrammed (Bit logic state = 1)
Indirect Access:
MOV
@R0, #data
; R0 contains 90H
3.3 Data RAM Memory
The data RAM has 1024 bytes of internal memory. The
RAM can be addressed up to 64KB for external data
memory.
Register R0 points to 90H which is located in the upper
address range. Data in “#data” is written to RAM location
90H rather than port 1.
Direct Access:
MOV
90H, #data
; write data to P1
Data in “#data” is written to port 1. Instructions that write
directly to the address write to the SFRs.
To access the expanded RAM, the EXTRAM bit must be
cleared and MOVX instructions must be used. The extra
768 bytes of memory is physically located on the chip and
logically occupies the first 768 bytes of external memory
(addresses 000H to 2FFH).
When EXTRAM = 0, the expanded RAM is indirectly
addressed using the MOVX instruction in combination
with any of the registers R0, R1 of the selected bank or
DPTR. Accessing the expanded RAM does not affect
ports P0, P3.6 (WR#), P3.7 (RD#), or P2. With
EXTRAM = 0, the expanded RAM can be accessed as
in the following example.
©2007 Silicon Storage Technology, Inc.
S71273-03-000
1/07
13
SST [ SILICON STORAGE TECHNOLOGY, INC ]
