IMX51A 查看數據表（PDF） - Freescale Semiconductor

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IMX51A

i.MX51A Automotive and Infotainment Applications Processors

Freescale Semiconductor 

Signal Name

VREF

VREFOUT

VREG

XTAL/EXTAL

JTAG

JTAG_TCK

JTAG_TMS

JTAG_TDI

JTAG_TDO

JTAG_TRSTB

JTAG_DE_B

JTAG_MOD

IOMUX Configuration for Boot Media

Table 3. Special Signal Considerations (continued)

Remarks

When using VREF with DDR-2 I/O, the nominal 0.9 V reference voltage must be half of the

NVCC_EMI_DRAM supply. The user must tie VREF to a precision external resistor divider. Use a

1 kΩ 0.5% resistor to GND and a 1 kΩ 0.5% resistor to NVCC_EMI_DRAM. Shunt each resistor

with a closely-mounted 0.1 µF capacitor.

To reduce supply current, a pair of 1.5 kΩ 0.1% resistors can be used. Using resistors with

recommended tolerances ensures the ± 2% VREF tolerance (per the DDR-2 specification) is

maintained when four DDR-2 ICs plus the i.MX51 are drawing current on the resistor divider.

Note: When VREF is used with mDDR this signal must be tied to GND.

This signal determines the Triple Video DAC (TVDAC) reference voltage. The user must tie

VREFOUT to an external 1.05 kΩ 1% resistor to GND.

This regulator is no longer used and should be floated by the user.

The user should tie a fundamental-mode crystal across XTAL and EXTAL. The crystal must be

rated for a maximum drive level of 100 μW or higher. An ESR (equivalent series resistance) of

80 Ω or less is recommended. Freescale BSP (Board Support Package) software requires 24 MHz

on EXTAL.

The crystal can be eliminated if an external 24 MHz oscillator is available. In this case, EXTAL must

be directly driven by the external oscillator and XTAL is floated. The EXTAL signal level must swing

from NVCC_OSC to GND. If the clock is used for USB, then there are strict jitter requirements: <

50 ps peak-to-peak below 1.2 MHz and < 100 ps peak-to-peak above 1.2 MHz for the USB PHY.

The COSC_EN bit in the CCM (Clock Control Module) must be cleared to put the on-chip oscillator

circuit in bypass mode which allows EXTAL to be externally driven. COSC_EN is bit 12 in the CCR

register of the CCM.

Table 4. JTAG Controller Interface Summary

I/O Type

Input

Input

Input

3-state output

Input

Input/open-drain output

Input

On-chip Termination

100 kΩ pull-down

47 kΩ pull-up

47 kΩ pull-up

Keeper

47 kΩ pull-up

47 kΩ pull-up

100 kΩ pull-down

3 IOMUX Configuration for Boot Media

The information provided in this section describes the contacts assigned for each type of bootable media.

It also includes data about the clocks used during boot flow and their frequencies. Signals that can be

multiplexed appear in tables throughout this section. See the IOMUXC chapter in the MX51 Reference

Manual for details about how to program the IOMUX controller.

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

Freescale Semiconductor

13

Preliminary—Subject to Change Without Notice

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