Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 370

External Signals
Table 12-3. Configuration-Dependent Signal Behavior During Reset
Signal Function Determined at Reset by
SRESET HRESET (or PORESET)
Previous SIUMCR default values only
programming of
SIUMCR
SIUMCR default values as
driven by the hard reset
configuration word
1
After a hard reset, this signal function is actually inactive until the user selects the function by programming the
SIUMCR.
12.4 Active Pull-Up Buffers
An active pull-up buffer is a special variety of a bidirectional three-state buffer with the following
properties:
• When enabled as an output and driving low, it behaves as a normal output driver (that is, the pin is
constantly driven low).
• When enabled as an output and driving high, it drives high until an internal detection circuit
determines that the output has reached the logic high threshold and then stops driving (that is, the
pin switches to high impedance).
• When disabled as an output or functioning as an input, it is not driven.
Due to the behavior of the buffer when being driven high, a pull-up resistor is required externally to
function as a 'bus keep' for these shared signals in periods when no drivers are active and to keep the buffer
12-40
KR/RETRY/IRQ4/SPKROUT
ALE_B/DSCK/AT1
IP_B[0:1]/IWP[0:1]/VFLS[0:1]
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Pin
BDIP/GPL_B5 BDIP: high impedance
GPL_B5: high
RSV/IRQ2 IRQ2: high impedance
RSV: high
CR/IRQ3 IRQ3: high impedance
CR: high
IRQ4: high impedance
KR/RETRY: high impedance
SPKROUT: low
FRZ/IRQ6 FRZ: low
IRQ6: high impedance
ALE_B: low
DSCK/AT1: high impedance
IP_B[0:1]: high impedance
IWP[0:1]: high
VFLS[0:1]: low
IP_B3/IWP2/VF2 IP_B3: high impedance
IWP2: high
VF2: low
IP_B4/LWP0/VF0 IP_B4: high impedance
LWP0: high
VF0: low
IP_B5/LWP1/VF1 IP_B5: high impedance
LWP1: high
VF1: low
Signal Behavior
1
1
1
1
1
1
Freescale Semiconductor