DS87C520_1 Datasheet, PDF (22/42 Pages) Dallas Semiconductor – EPROM/ROM High-Speed Micro

INTERRUPT SOURCES AND PRIORITIES Table 9
NAME
DESCRIPTION
VECTOR
PFI
Power-Fail Interrupt
33h
INT0
External Interrupt 0
03h
TF0
Timer 0
0Bh
INT1
External Interrupt 1
13h
TF1
Timer 1
1Bh
SCON0
TI0 or RI0 from serial port 0
23h
TF2
Timer 2
2Bh
SCON1
TI1 or RI1 from serial port 1
3Bh
INT2
External Interrupt 2
43h
INT3
External Interrupt 3
4Bh
INT4
External Interrupt 4
53h
INT5
External Interrupt 5
5Bh
WDTI
Watchdog Time -Out Interrupt
63h
NATURAL
PRIORITY
1
2
3
4
5
6
7
8
9
10
11
12
13
DS87C520/DS83C520
8051/DALLAS
DALLAS
8051
8051
8051
8051
8051
8051
DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
TIMED ACCESS PROTECTION
It is useful to protect certain SFR bits from an accidental write operation. The Timed Access procedure
stops an errant CPU from accidentally changing these bits. It requires that the following instructions
precede a write of a protected bit.
MOV
MOV
0C7h, #0Aah
0C7h, #55h
Writing an AAh then a 55h to the Timed Access register (location C7h) opens a 3-cycle window for write
access. The window allows software to modify a protected bit(s). If these instructions do not
immediately precede the write operation, then the write will not take effect. The protected bits are:
EXIF.0
WDCON.6
WDCON.1
WDCON.0
WDCON.3
ROMSIZE.2
ROMSIZE.1
ROMSIZE.0
BGS
POR
EWT
RWT
WDIF
RMS2
RMS1
RMS0
Band-gap Select
Power-on Reset flag
Enable Watchdog Reset
Restart Watchdog
Watchdog Interrupt Flag
ROM size select 2
ROM size select 1
ROM size select 0
EPROM PROGRAMMING
The DS87C520 follows standards for a 16 kB EPROM version in the 8051 family. It is available in a UV-
erasable, ceramic windowed package and in plastic packages for one-time user-programmable versions.
The part has unique signature information so programmers can support its specific EPROM options.
ROM-specific features are described later in this data sheet.
Most commercially available device programmers will directly support Dallas Semiconductor
microcontrollers. If your programmer does not, please contact the manufacturer for updated software.
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