Reset Configuration - Freescale Semiconductor PowerQUICC MPC885 Reference Manual

External Signals
The purpose of active pull-up buffers is to allow access to zero wait-state logic that drives a shared signal
on the clock cycle immediately following a cycle in which the signal is driven by the MPC885. In other
words, it eliminates the need for a bus turn-around cycle.
12.5 Internal Pull-Up and Pull-Down Resistors
The TDI/DSDI, TMS, and TRST pins have internal pull-up resistors.
If RSTCONF is pulled down during hardware reset (initiated by HRESET or PORESET), the data bus
D[0:31] is pulled down with internal pull-down resistors. These internal pull-down resistors are to provide
a logic-zero default for these pins when programming the hard reset configuration word (see
Section 11.3.1.1, "Hard Reset Configuration Word"). These internal pull-down resistors are disconnected
after HRESET is negated.
No other pins have internal pullups or pulldowns.
Resistance values for internal pull-up and pull-down resistors are not specified because their values may
vary due to process variations and shrinks in die size, and they are not tested. Typical values are on the
order of 5 kΩ but can vary by approximately a factor of 2.
12.6 Recommended Basic Pin Connections
The following sections provide recommended pin connections.
12.6.1

Reset Configuration

Some external pin configurations are determined at reset by the hard reset configuration word. Thus, some
decisions regarding system configuration (for example, location of BDM pins) should be made before
required application of pull-up and pull-down resistors can be determined.
RSTCONF should be grounded if the hard reset configuration word is used to configure the MPC885 or
should be connected to VCC if the default configuration is used.
Pull-up resistors should not be used on D[0:31] to set the hard reset configuration word, as the values of
the internal pull-down resistors are not specified or guaranteed. To change a data bus signal from its default
logic low state during reset, actively drive that signal high.
MODCK[1:2] must be used to determine the default clocking mode for the MPC885. After power-on reset,
the MODCK[1:2] pins change function and become outputs. Thus, if these alternate functions are also
desired, then the MODCK[1:2] configuration should be set with three-state drivers that turn off after
PORESET is negated. However, if the MODCK[1:2] pins alternate output functions are not used in the
system, they can be configured with pull-up and pull-down resistors.
12.6.1.1 Bus Control Signals and Interrupts
Signals with open-drain buffers and active pull-up buffers (HRESET, SRESET, TEA, TS, TA, BI, and BB)
must have external pull-up resistors.
MPC885 PowerQUICC Family Reference Manual, Rev. 2
12-42 Freescale Semiconductor