DS89C420 Datasheet, PDF (43/59 Pages) Dallas Semiconductor – Ultra-High-Speed Microcontroller

DS89C420
vector using the RETI instruction, the next address is the one that immediately follows the instruction that
invoked the idle mode. Any processor resets also remove the idle mode.
Stop Mode
The stop mode disables all circuits within the processor. All on-chip clocks, timers, and serial port
communication are stopped, and no processing is possible.
Stop mode is invoked by setting the STOP bit (PCON.1) to logic 1. The processor enters the stop mode
on the instruction that sets the bit. The processor can exit stop mode by using any of the six external
interrupts that are enabled.
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.
43 of 59