DS83C520_07 Datasheet, PDF (25/43 Pages) Dallas Semiconductor – EPROM/ROM High-Speed Microcontrollers

DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers
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
Bandgap 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 16kB 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.
PROGRAMMING PROCEDURE
The DS87C520 should run from a clock speed between 4MHz and 6MHz when being programmed. The
programming fixture should apply address information for each byte to the address lines and the data
value to the data lines. The control signals must be manipulated as shown in Table 9. The diagram in
Table 5 shows the expected electrical connection for programming. Note that the programmer must apply
addresses in demultiplexed fashion to Ports 1 and 2 with data on Port 0. Waveforms and timing are
provided in the Electrical Specifications section.
Program the DS87C520 as follows:
1) Apply the address value,
2) Apply the data value,
3) Select the programming option from Table 9 using the control signals,
4) Increase the voltage on V_PP from 5V to 12.75V if writing to the EPROM,
5) Pulse the PROG signal five times for EPROM array and 25 times for encryption table, lock bits, and
other EPROM bits,
6) Repeat as many times as necessary.
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