DS89C420_05 Datasheet, PDF (18/47 Pages) Maxim Integrated Products – Ultra-High-Speed Microcontroller

DS89C420 Ultra-High-Speed Microcontroller
Table 2. SFR Reset Value
REGISTER
P0
SP
DPL
DPH
DPL1
DPH1
DPS
PCON
TCON
TMOD
TL0
TL1
TH0
TH1
CKCON
P1
EXIF
CKMOD
SCON0
SBUF0
ACON
P2
IE
SADDR0
SADDR1
P3
IP1
IP0
SADEN0
SADEN1
SCON1
SBUF1
ROMSIZE
PMR
STATUS
TA
T2CON
T2MOD
RCAP2L
RCAP2H
TL2
TH2
PSW
FCNTL
FDATA
WDCON
ACC
EIE
B
EIP1
EIP0
ADDR
80h
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
8Dh
8Eh
90h
91h
96h
98h
99h
9Dh
A0h
A8h
A9h
AAh
B0h
B1h
B8h
B9h
BAh
C0h
C1h
C2h
C4h
C5h
C7h
C8h
C9h
CAh
CBh
CCh
CDh
D0h
D5h
D6h
D8h
E0h
E8h
F0h
F1h
F8h
BIT 7
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
0
0
0
1
0
0
0
1
1
1
0
0
0
0
1
1
0
1
0
1
0
0
0
0
0
1
0
0
0
1
0
1
1
BIT 6
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
0
0
0
1
0
0
0
1
0
0
0
0
0
0
1
0
0
1
0
1
0
0
0
0
0
0
0
Special
0
1
0
1
1
BIT 5
1
0
0
0
0
0
0
Special
0
0
0
0
0
0
0
1
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
1
0
0
1
0
1
0
0
0
0
0
1
0
0
0
1
0
1
1
BIT 4
1
0
0
0
0
0
0
Special
0
0
0
0
0
0
0
1
0
0
0
0
1
1
0
0
0
1
0
0
0
0
0
0
1
0
1
1
0
1
0
0
0
0
0
1
0
Special
0
0
0
0
0
BIT 3
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
Special
0
0
0
1
1
0
0
0
1
0
0
0
0
0
0
0
0
0
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
BIT 2
1
1
0
0
0
0
1
0
0
0
0
0
0
0
0
1
Special
1
0
0
1
1
0
0
0
1
0
0
0
0
0
0
1
0
0
1
0
1
0
0
0
0
0
0
0
Special
0
0
0
0
0
BIT 1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
Special
1
0
0
1
1
0
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
Special
0
0
0
0
0
BIT 0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
1
0
0
1
1
0
0
0
1
0
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
MEMORY ORGANIZATION
There are three distinct memory areas in the DS89C420: scratchpad registers, program memory, and data
memory. All registers are located on-chip but the program and data memory spaces can either be on-chip, off-chip,
or both. There are 16kB of on-chip program memory implemented in flash memory and 1kB of on-chip data
memory space that can be configured as program space using the PRAME bit in the ROMSIZE feature. The
DS89C420 uses a memory-addressing scheme that separates program memory from data memory. The program
and data segments can be overlapped since they are accessed in different ways. If the maximum address of on-
chip program or data memory is exceeded, the DS89C420 performs an external memory access using the
expanded memory bus. The PSEN signal goes active-low to serve as a chip enable or output enable when
performing a code fetch from external program memory. MOVX instructions activate the RD or WR signal for
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