MPC875CVR133 datasheet(15/84 Pages) FREESCALE

15 / 84 page

MPC875/MPC870 PowerQUICC™ Hardware Specifications, Rev. 4

Freescale Semiconductor

Mandatory Reset Configurations

One consequence of multiple power supplies is that when power is initially applied, the voltage rails ramp

up at different rates. The rates depend on the nature of the power supply, the type of load on each power

supply, and the manner in which different voltages are derived. The following restrictions apply:

•VDDL must not exceed VDDH during power up and power down

•VDDL must not exceed 1.9 V, and VDDH must not exceed 3.465 V

These cautions are necessary for the long-term reliability of the part. If they are violated, the electrostatic

discharge (ESD) protection diodes are forward-biased, and excessive current can flow through these

diodes. If the system power supply design does not control the voltage sequencing, the circuit shown in

Figure 4 can be added to meet these requirements. The MUR420 Schottky diodes control the maximum

potential difference between the external bus and core power supplies on power up, and the 1N5820 diodes

regulate the maximum potential difference on power down.

Figure 4. Example Voltage Sequencing Circuit

Mandatory Reset Configurations

The MPC875/MPC870 requires a mandatory configuration during reset.

If hardware reset configuration word (HRCW) is enabled, the HRCW[DBGC] value needs to be set to

binary X1 in the HRCW and the SIUMCR[DBGC] should be programmed with the same value in the boot

code after reset. This can be done by asserting the RSTCONF during HRESET assertion.

If HRCW is disabled, the SIUMCR[DBGC] should be programmed with binary X1 in the boot code after

reset by negating the RSTCONF during the HRESET assertion.

The MBMR[GPLB4DIS], PAPAR, PADIR, PBPAR, PBDIR, PCPAR, and PCDIR need to be configured

with the mandatory values in Table 7 in the boot code after the reset is negated.

Table 7. Mandatory Reset Configuration of MPC875/MPC870

Field

Value

(Binary)

HRCW (Hardware reset configuration word)

HRCW[DBGC]

SIUMCR (SIU module configuration register)

SIUMCR[DBGC]

MBMR (Machine B mode register)

MBMR[GPLB4DIS}

PAPAR (Port A pin assignment register)

PAPAR[5:9]

PAPAR[12:13]

VDDH

VDDL

1N5820

MUR420

MPC875CVR133 Datasheet(PDF) 15 Page - Freescale Semiconductor, Inc