DS80C320-MCG Datasheet, PDF (173/175 Pages) Dallas Semiconductor – High-Speed Microcontroller User Guide

SECTION 17: TROUBLESHOOTING
High-Speed Microcontroller User’s Guide
DEVICE OPERATES AT 1/3 OF CRYSTAL SPEED
The High-Speed Microcontroller Family operates from the primary or fundamental mode of the external
crystal. Many off-the-shelf high-frequency crystals are specified to operate from their third overtone.
When used with a High-Speed Microcontroller, these crystals will resonate in their primary mode, which
will appear to be 1/3 of the rated crystal speed. Make sure that any crystals used will operate at their
rated speed in primary mode.
DEVICE RESETS FOR NO REASON
During the debugging process, it may be necessary to isolate the cause of an unexpected device reset.
Because resets are initiated by a limited number of sources, it is relatively easy to determine their source
by interrogating a few bits. These bits should be interrogated early in the code following a reset to
determine its source. As a debug tool, software could set the state of one or more port pins to indicate the
type of reset to the designer. Note that power supply problems or glitches will appear as unplanned
power-on resets.
SOURCE
Power–on reset
Watchdog reset
External reset
POR BIT
WDCON.6
1
0
0
WTRF BIT
WDCON.3
0
1
0
ACCESS TO INTERNAL MOVX SRAM IS UNSUCCESSFUL
The internal MOVX SRAM available on some members of the High-Speed Microcontroller Family is
disabled after any reset. To enable the on-chip SRAM, the software should configure the Data Memory
Enable bits (PMR.1-0) as needed.
When V_CC drops below V_BAT , access to the SRAM is disabled to prevent corruption of the data. If the
battery voltage is greater than V_RST, this means that the processor may continue to operate while SRAM
access is denied. Make sure that the battery voltage remains below the minimum V_RST.
REAL-TIME CLOCK DOES NOT OPERATE OR KEEP ACCURATE TIME.
The state of the real-time clock (RTC) used on the DS87C530 is undefined following a no-battery reset or
battery attach. The RTC oscillator must be enabled by setting the RTCE bit (RTCC.0) for the RTC to
work.
The RTC is guaranteed to a minimum accuracy of ± 2 minutes per month over the rated temperature and
voltage specifications. If the time is found to be less accurate than this, it is most likely due to the
selection of crystal. Make sure that the RTC crystal is 32.768 kHz, and either 12.5 pF or 6 pF
capacitance. The 12/6 bit (TRIM.6) setting should correspond to the crystal in use. Unlike other crystals,
external load capacitors should not be used with the RTC. These will seriously distort the accuracy of the
clock. Additional information on design considerations with the RTC can be found in Applications Note
79, Using the DS87C530 Real Time Clock.
173 of 175