PXR40RM Datasheet, PDF (67/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

Chapter 3
Signal Descriptions
This chapter describes the external device signals, including a table of signal properties, detailed
descriptions of the available signals, and the I/O pin power/ground segmentation.
3.1 Pin Function Selection
3.1.1 Pad Configuration Register (PCR) PA Definition
Most pins (balls) on the package support more than one function. Unlike prior devices in this class, the
required pin function on this device is selected by a fixed size of the PA bit field in each SIU_PCR. The
PA width is fixed at 3 bits. The pin function categories are:
Table 3-1. SIU_PCR PA Definition
PA
Function Category
000 GPIO
001 Primary Function
010 Alternate function 1 (A1)
011 Alternate function 2 (A2)
100 Alternate function 3 (A3)
Pins that do not require selection of a function by modifying the PA field have a hard-wired value
corresponding to the appropriate function available at the pin. All PA values might not be used. A
definition of which values are used is provided in the SIU chapter’s PCR settings table. The “Primary
Function” name is retained from previous MPC5xxx designs and indicates the name used on the ball map.
The name “GPIO” is also retained for clarity. The remaining function names are new and have been chosen
for simplicity and clarity.
3.1.2 LVDS Signal Selection
A pin (ball) that is driven by a signal from a 5V pad or from an LVDS pad has a single PCR controlling
both signals. Different values of PA select either the 5V signal or the LVDS signal. Note that a single LVDS
pad supplies two signals — a “true” and a “complement” output. This means that one LVDS pad drives
two balls, but each ball has a separate PCR (and PA field). The two LVDS signals are enabled only when
the PA values in both PCRs are set to select LVDS operation. Both LVDS signals are deselected when
either PA is set to a value that deselects its LVDS signal. The ball that has its PA field still set to LVDS will
go to an undriven state until its PA field is updated to a non-LVDS value.
PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
3-1