i.MX25 Applications Processor for Consumer and Industrial Products, Rev. 10
10
Freescale Semiconductor
MESH_C, MESH_D Wire-mesh tamper detect pins that can be routed at the PCB board to detect attempted tampering of a
protected wire. When security measures are implemented, MESH_C should be pulled-up or connected to
NVCC_DRYICE and triggers a tamper event when floating or when connected to MESH_D. MESH_D
should be pulled-down or connected to GND and triggers an event when floating or connected to
MESH_C. These pins can be left unconnected if the DryIce security features are not being used.
NVCC_DRYICE
This is the DryIce power supply output. The supply source is QVDD when the i.MX25 is in run mode. When
i.MX25 is in reduced power mode, the DryIce supply source is the BATT_VDD supply. This pin can be
used to power external DryIce components (external tamper detect, wire-mesh tamper detect). In order
to guarantee the power-loss protection feature which guarantees that RTC and/or secure keys be
maintained after power-off an external capacitor no less than 4 F must be connected to this supply output
pin. A 4.7 F capacitor is recommended.
OSC_BYP
The 32 kHz oscillator bypass-control pin. If this signal is pulled down, then OSC32K_EXTAL and
OSC32K_XTAL analog pins should be tied to the external 32.768 kHz crystal circuit. If on the other hand
the signal is pulled up, then the external 32 kHz oscillator output clock must be connected to
OSC32K_EXTAL analog pin, and OSC32K_XTAL can be no connect (NC).
OSC32K_EXTAL
OSC32K_XTAL
These analog pins are connected to an external 32 kHz CLK circuit depending on the state of OSC_BYP
pin (see the description of OSC_BYP under the preceding bullet). The 32 kHz reference CLK is required
for normal operation.
POWER_FAIL
An interrupt from PMIC, which should be connected to a low-battery detection circuit. This signal is
internally connected to an on-chip 100 k
Ω pull-down device. If there is no low-battery detection, then users
can tie this pin to GND through a pull-down resistor, or leave the signal as NC. This pin can also be
configured to work as a normal GPIO.
REF
External ADC reference voltage. REF may be tied to GND if the user plans to only use the internally
generated 2.5 V reference supply.
SJC_MOD
Must be externally connected to GND for normal operation. Termination to GND through an external
pull-down resistor (such as 1 k
Ω) is allowed, but the value should be much smaller than the on-chip 100
k
Ω pull-up.
TAMPER_A,
TAMPER _B
DryIce external tamper detect pins, active high. If TAMPER_A or TAMPER_B is connected to
NVCC_DRYICE, then external tampering is detected. These pins can be left unconnected if the DryIce
security features are not being used.
TEST_MODE
For Freescale factory use only. This signal is internally connected to an on-chip pull-down device. Users
must either float this signal or tie it to GND.
UPLL_BYPCLK
Primarily for Freescale factory use. There is no internal on-chip pull-up/down on this pin, so it must be
externally connected to GND or VDD. Aside from factory use, this pin can also be configured (through
muxing) to work as a normal GPIO.
USBPHY1_RREF
Determines the reference current for the USB PHY1 bandgap reference. An external 10 k
Ω 1% resistor to
GND is required.
USBPHY2_DM
USBPHY2_DP
The output impedance of these signals is expected at 10
Ω. It is recommended to also have on-board 33 Ω
series resistors (close to the pins).
Table 4. Signal Considerations (continued)
Signal
Description