DETAILED DESCRIPTION
The DS89C420 is pin compatible with all three packages of the standard 8051 and includes standard resources such as three timer/counters, four 8-bit I/O ports, and a serial port.
It features 16kB of in-system programmable flash memory, which can be programmed in-system from an I/O port using a built-in program memory loader.
It can also be loaded externally using standard commercially available
programmers.
Besides greater speed, the DS89C420 includes 1kB of data RAM, a second full-hardware serial port,
seven additional interrupts, two more levels of interrupt priority, programmable watchdog timer, brown-
out monitor, and power-fail reset. The device also provides dual data pointers (DPTRs) to speed up
block-data memory moves. This feature is further enhanced with a new selectable automatic
increment/decrement and toggle-select operation. The speed of MOVX data memory access can be
adjusted by adding stretch values up to 10 machine cycle times for flexibility in selecting external
memory and peripherals.
A power management mode (PMM) significantly consumes less power by slowing the CPU execution
rate from 1 clock period per cycle to 1024 clock periods per cycle.
A selectable switchback feature can automatically cancel this mode to enable a normal speed response to interrupts.
The EMI reduction feature disables the ALE signal when the processor is not accessing external memory.