DS89C420_05 Datasheet, PDF (42/47 Pages) Maxim Integrated Products – Ultra-High-Speed Microcontroller

DS89C420 Ultra-High-Speed Microcontroller
An external reset by the RST pin unconditionally exits the processor from stop mode. If the BGS bit is set to logic 1,
the bandgap provides a reset while in stop mode if V_CC should drop below the V_RST level. If BGS is 0, no reset is
generated if V_CC drops below V_RST.
When the stop mode is removed, the processor waits for 65,536 clock cycles for the internal flash memory to warm
up before starting normal execution. Also, the processor waits for the crystal warmup period if not using the ring
oscillator.
SERIAL I/O
The DS89C420 provides a serial port (UART) that is identical to the 80C52. In addition, it includes a second
hardware serial port that is a full duplicate of the standard one. This port optionally uses pins P1.2 (RXD1) and
P1.3 (TXD1) and has duplicate control functions included in new SFR locations.
Both ports can operate simultaneously but can be at different baud rates or even in different modes. The second
serial port has similar control registers (SCON1 at C0h, SBUF1 at C1h) as the original. The new serial port can
only use timer 1 for timer-generated baud rates.
Control for serial port 0 is provided by the SCON0 register while its I/O buffer is SBUF0. Registers SCON1 and
SBUF1 provide the same functions for the second serial port. A full description of the use and operation of both
serial ports is in the Ultra-High-Speed Flash Microcontroller User’s Guide.
INSTRUCTION SET
The DS89C420 instructions are 100% binary compatible with the industry standard 8051, and are only different in
the number of machine cycles used for the instructions. Some special conditions and features should be
considered when analyzing the DS89C420 instruction set. Full details are given in the Ultra-High-Speed Flash
Microcontroller User’s Guide.
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