Maxim Integrated Secure Microcontroller - Manual (Page 179)

Secure Microcontroller User’s Guide
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INT0 is stuck low on DS2252T.
The DS2252T incorporates an RTC with interrupt capability. The
INTP output of the RTC is connected
to the
INTO pin of the DS5002FP microcontroller and also the INTO pin of the SIMM. If an RTC
interrupt occurs, this will pull the
INTO signal low. If the system is not expecting the INTO signal to be
active, this can appear as the
INTO signal “stuck” low. Because the state of the RTC alarm is undefined
after the freshness seal is broken, the device can power up with the interrupt active, holding the
INTO
signal low. This condition can also occur if software accidentally activates the alarm during normal
operation, or if an alarm occurs during data retention mode. To clear this condition, clear the RTC alarm
(if desired) as part of the power-on reset sequence, before interrupts are enabled.
Problems with the DS5000TK Evaluation Kit.
This is a general category of complaint that could be related to problems with the target microcontroller,
the PC software or COM port, or the DS5000TK hardware. Below are listed some of the most common
problems and suggested remedies.
DS5000TK Evaluation Kit does not respond to PC host software.
1) V
CC
and GND must be supplied via the ribbon cable. An external crystal (via ribbon cable) is required
to run a program. The DS5000TK hardware internal oscillator is used only for program loading.
2) Cable is broken or a standard phone cable has been used. A standard phone cable has the wrong pin
out of the DS5000TK.
3) Incorrect COM port has been selected.
4) The device is not locked into its ZIF socket.
Communication fails on a DS5000TK.
1) The ribbon cable represents a significant stray capacitance to the crystal pins. The crystal may be
running at the wrong frequency. Observing ALE, which should be 1/6 of the crystal, can check this. If
it is not, adjust the capacitors to get the correct frequency.
2) The A/B switch is in the wrong position. In position A, the serial port is routed to the target system. In
position B, it goes back to the PC COM port. Position B is the correct position for use when loading
the device.
DEMODS5T program does not work.
If the DEMODS5T program does not work, this is normally caused by the serial communication
problems mentioned above. For the demo, the crystal must oscillate at 11.0592MHz. Also, the A/B
switch must be in position B so the microcontroller communicates with the PC through the serial port
while running code.
18.7 Do’s and Don’ts
This section highlights common mistakes and offers helpful hints.
Don’ts
RC Resets. Do not use an RC circuit for a power-on reset. The secure microcontroller family does this
internally. If the traditional RC circuit is used without a diode, it will expose the RST pin to -5V if power
falls faster than the RC time constant.
Battery-Backed Signals. Do not connect battery-backed chip enables or signals to nonbacked devices.
This produces a drain on the battery. On the DS5001 and DS5002,
PE1 and PE2 as a well as CE1 - 4 are