DS89C420_02 Datasheet, PDF (18/58 Pages) Maxim Integrated Products – Ultra-High-Speed Microcontroller

DS89C420
The read/write accessibility is determined by the state of the lock bits, which can be verified directly by
the ROM loader. In the ROM loader mode, a mass-erase operation also erases the memory bank select
and sets it to the default state. Otherwise, the memory bank select cannot be altered in the ROM loader
mode.
Flash programming is executed by a series of internal flash commands that are derived (by the built- in
ROM loader) from data transmitted over the serial interface from a host PC. ROM loader software for
creating required commands (for flash or external data memory) from the host PC is available from
Dallas Semicond uctor, titled “Loader 420.”
Full details of the ROM loader software and its implementation are given in the DS89C420 User’s Guide.
PARALLEL PROGRAMMING
The DS89C420 allows parallel programming of its internal flash memory compatible with standard flash
or EPROM programmers. In parallel programming mode, a mass-erase command is used to erase all
memory locations in the 16kB program memory, the security block, and the memory bank select. Erasing
the memory bank select sets it to the default state; the memory bank select cannot be altered otherwise. If
lock bit LB2 has not been programmed, the program code can be read back for verification. The state of
the lock bits can also be verified directly in the parallel programming mode. One instruction is used to
read signature information (at addresses 30, 31, and 60h). Separate instructions are used for the option
control register.
The following sequence can be used to program the flash memory in the parallel programming mode:
1) The DS89C420 is powered up and running at a clock speed between 4MHz and 6MHz.
2) Set RST = EA = 1 and PSEN = 0.
3) Apply the appropriate logic combination to pins P2.6, P2.7, P3.6, and P3.7 to select one of the flash
instructions shown in Table 8.
− For program operation, apply the desired address to pins P1.7:0 and P2.5:0. Data is written to
port 0.
− For verify operation, apply the desired address to pins P1.7:0 and P2.5:0. Data is read at port 0.
4) Pulse ALE/ PROG once to perform an erase/program operation.
5) Repeat steps 3 and 4 as necessary.
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