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IMX51A

i.MX51A Automotive and Infotainment Applications Processors

Freescale Semiconductor 

Features

Table 2. i.MX51A Digital and Analog Modules (continued)

Block

Mnemonic

Block Name Subsystem

Brief Description

WDOG-2 Watch Dog Timer

(TZ)

(TrustZone) Peripherals

XTALOSC Crystal

Clocking

Oscillator I/F

The TrustZone Watchdog (TZ WDOG) timer module protects against TrustZone

starvation by providing a method of escaping normal mode and forcing a switch

to the TZ mode. TZ starvation is a situation where the normal OS prevents

switching to the TZ mode. This situation should be avoided, as it can

compromise the system’s security. Once the TZ WDOG module is activated, it

must be serviced by TZ software on a periodic basis. If servicing does not take

place, the timer times out. Upon a time-out, the TZ WDOG asserts a TZ mapped

interrupt that forces switching to the TZ mode. If it is still not served, the TZ

WDOG asserts a security violation signal to the CSU. The TZ WDOG module

cannot be programmed or deactivated by a normal mode SW.

The XTALOSC module allows connectivity to an external crystal.

2.1 Special Signal Considerations

Table 3 lists special signal considerations for the i.MX51. The signal names are listed in alphabetical order.

The package contact assignments are found in Section 5, “Package Information and Contact

Assignments.” Signal descriptions are defined in the i.MX51 reference manual.

Table 3. Special Signal Considerations

Signal Name

CKIH1, CKIH2

CLK_SS

COMP

FASTR_ANA and

FASTR_DIG

GPANAIO

GPIO_NAND

Remarks

Inputs feeding CAMPs (Clock Amplifiers) that have on-chip ac coupling precluding the need for

external coupling capacitors. The CAMPs are enabled by default, but the main clocks feeding the

on-chip clock tree are sourced from XTAL/EXTAL by default. Optionally, the use of a low jitter

external oscillators to feed CKIH1 or CKIH2 (while not required) can be an advantage if low jitter

or special frequency clock sources are required by modules driven by CKIH1 or CKIH2. See CCM

chapter in the i.MX51 reference manual for details on the respective clock trees.

After initialization, the CAMPs could be disabled (if not used) by CCM registers (CCR CAMPx_EN

field). If disabled, the on-chip CAMP output is low; the input is irrelevant. If unused, the user should

tie CKIH1/CKIH2 to GND for best practice.

Clock Source Select is the input that selects the default reference clock source providing input to

the DPLLs. To use a reference in the megahertz range per Table 8, tie CLK_SS to GND to select

EXTAL/XTAL. To use a reference in the kilohertz range per Table 59, tie CLK_SS to NVCC_PER3

to select CKIL. After initialization, the reference clock source can be changed (initial setting is

overwritten).

Note: Because this input has a keeper circuit, Freescale recommends tying this input to directly

to GND or NVCC_PER3. If a series resistor is used its value must be ≤ 4.7 kΩ.

The user should bypass this reference with an external 0.1 µF capacitor tied to GND. If TV OUT is

not used, float the COMP contact and ensure the DACs are powered down.

Note: Previous engineering samples required this reference to be bypassed to a positive supply.

These signals are reserved for Freescale manufacturing use only. User must tie both connections

to GND.

This signal is reserved for Freescale manufacturing use only. Users should float this output.

This is a general-purpose input/output (GPIO3_12) on the NVCC_NANDF_A power rail.

i.MX51A Automotive and Infotainment Applications Processors, Rev. 2

Freescale Semiconductor

11

Preliminary—Subject to Change Without Notice

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