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High-Speed Microcontroller User’s Guide
SECTION 17: TROUBLESHOOTING
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.
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High-Speed Microcontroller User’s Guide
SERIAL PORT DOES NOT WORK
The serial port is not a complicated peripheral, but there are many elements that need to be initialized.
The following checklist is provided to help in debugging.
1. Have the appropriate port latch bits (P3.0, P3.1, P1.2, or P1.3) been set to 1 to enable the serial port
functions?
2. Has the correct timebase been selected? (4 clocks per tick or 12 clocks per tick)
3. Is the appropriate timer reload value loaded?
4. Is the appropriate timer mode selected?
5. Is the appropriate timer running by setting TR0, TR1, or TR2 bits?
6. Is the correct serial port mode selected?
7. If desired, is the serial port doubler bit, SMOD, set? (PCON.7 or WDCON.7)
8. If desired, is the receive enable bit (REN_0 or REN_1) set?
9. Is the serial port interrupt enabled?
10. Is the global interrupt enable bit set?
HIGH-SPEED MICROCONTROLLER DOES NOT WORK IN EXISTING 8051
DESIGN
Although the High-Speed Microcontroller Family was designed as a drop in replacement for the 8051
family, occasionally a developer may notice problems when inserting into an existing design. Often these
problems are related to slow memory interfaces which cannot keep up with the increased throughput of
the faster microcontroller. In addition, software timing loops will run faster, possibly changing program
operation. These and other effects are described in Application Note 56 (The DS80C320 as a Drop-In
Replacement for the 8032). Application Note 57 (DS80C320 Memory Interface Timing) discusses
memory interface timing for the DS80C320. Application Note 89 (High-Speed Micro Memory Interface
Timing) discusses interfacing other members of the High-Speed Microcontroller family to external
memory.
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