DS89C420_05 Datasheet, PDF (23/47 Pages) Maxim Integrated Products – Ultra-High-Speed Microcontroller

Figure 7. Interfacing the Bootloader to a PC
DS89C420 Ultra-High-Speed Microcontroller
PARALLEL PROGRAMMING
The microcontroller also supports a programming mode such as that used by commercial device programmers.
This mode is of little utility in normal applications and is only used by commercial device programmers. For
information on this mode, contact our technical support department at [e-mail].
ON-CHIP MOVX DATA MEMORY
On-chip data memory is provided by the 1kB SRAM and occupies addresses 0000h through 03FFh. The internal
data memory is disabled after a power-on reset, and any MOVX instruction directs the data memory access to the
external data memory. To enable the internal data memory, software must configure the data memory enable bits
DME1 and DME0 (PMR.1-0). See “SFR Bit Descriptions” in the Ultra-High-Speed Flash Microcontroller User’s
Guide for data memory configurations. Once enabled, MOVX instructions with addresses inside the 1k range
access the on-chip data memory, and addresses exceeding the 1k range automatically access external data
memory.
An internal data memory cycle spans only one system clock period to support fast internal execution.
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