DS89C420_05 Datasheet, PDF (14/47 Pages) Maxim Integrated Products – Ultra-High-Speed Microcontroller

Figure 5. Block Diagram
DS89C420 Ultra-High-Speed Microcontroller
Control &
Sequencer
Internal
Registers
Decoder
IR
Internal Control Bus
Interrupt
CPU
SFRs
DPTR
DPTR1
SP
PC
AR Inc
AR
Address Bus
Serial I/O
Timer /
Counters
Watchdog Timer
&
Power Manager
Dallas Semiconductor
DS89C420
Clock &
Reset
1Kx 8
RAM
16K x 8
Flash
I/O Ports
Memory
Control
ROM
Loader
P0 P1 P2 P3
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, brownout 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.
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