DS80C390 Datasheet, PDF (22/58 Pages) Dallas Semiconductor – Dual CAN High-Speed Microprocessor

DS80C390
EMI REDUCTION
One of the major contributors to radiated noise in an 8051-based system is the toggling of ALE. The
microcontroller allows software to disable ALE when not used by setting the ALEOFF (PMR.2) bit to a
1. When ALEOFF = 1, ALE will automatically toggle during an off-chip MOVX. However, ALE will
remain static when performing on-chip memory access. The default state of ALEOFF is 0 so ALE
normally toggles at a frequency of XTAL/4.
PERIPHERAL OVERVIEW
The DS80C390 provides several of the most commonly needed peripheral functions in microcomputer-
based systems. New functions include a second serial port, power-fail reset, power-fail interrupt flag, and
a programmable watchdog timer. In addition, the microcontroller contains two Controller Area Network
(CAN) modules for industrial communication applications. Each of these peripherals is described below,
and more details are available in the User’s Guide.
SERIAL PORTS
The microcontroller 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 second port optionally uses
pins P1.2 (RXD1) and P1.3 (TXD1). It has duplicate control functions included in new SFR locations.
The second serial port can alternately be mapped to P5.2 and P5.3 to allow use of both serial ports in non-
multiplexed mode.
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, SBUF1) to the original. The new serial port can
only use Timer 1 for baud rate generation.
The SCON0 register provides control for serial port 0 while its I/O buffer is SBUF0. The registers
SCON1 and SBUF1 provide the same functions for the second serial port. A full description on the use
and operation of both serial ports may be found in the User’s Guide.
WATCHDOG TIMER
The Watchdog is a free running, programmable timer that can set a flag, cause an interrupt, and/or reset
the microcontroller if allowed to reach a preselected time-out. It can be restarted by software.
A typical application uses the watchdog timer as a reset source to prevent software from losing control.
The watchdog timer is initialized, selecting the time-out period and enabling the reset and/or interrupt
functions. After enabling the reset function, software must then restart the timer before its expiration or
hardware will reset the CPU. In this way if the code execution goes awry and software does not reset the
watchdog as scheduled, the processor is put in a known good state: reset.
Software can select one of four time-out values as controlled by the WD1 and WD0 bits. Time-out
values are precise since they are a function of the crystal frequency. When the Watchdog times out, it
sets the Watchdog Timer Reset Flag (WTRF=WDCON.2) which generates a reset if enabled by the
Enable Watchdog Timer Reset (EWT=WDCON.1) bit. Both the Enable Watchdog Timer Reset and the
Reset Watchdog Timer control bits are protected by Timed Access circuitry. This prevents errant
software from accidentally clearing or disabling the Watchdog.
The Watchdog interrupt is useful for systems that do not require a reset circuit. It will set the WDIF
(Watchdog interrupt) flag 512 clocks before setting the reset flag. Software can optionally enable this
interrupt source, which is independent of the watchdog reset function. The interrupt is common used
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