Table 5-6. Input-Output Usage (Continued)
Input/Output with
Internal
Pullup Resistors
Required
External
Resistor
750FX Signal
Name
Input/
Output
Active Level
Usage Group
Level Protect
Keeper
Comments
Notes
1, 3, 4
TT[0:4]
High
—
Input/Output
—
Transfer Attributes
Power Supply
V
DD
WT
Low
Output
Transfer Attributes
Keeper
1, 3, 4
Notes:
1. Depends on the system design. The electrical characteristics of the 750FX do not add additional constraints to the system design, so whatever is done with the net will depend on the system require-
ments.
2. HRESET, SRESET, and TRST are signals used for ESP and RISCWatch to enable proper operation of the debuggers. Logical AND gates should be placed between these signals and PowerPC
750FX RISC Microprocessor. (Refer to Figure 5-7 on page 48.)
3. The 750FX provides protection from meta-stability on inputs through the use of a “keeper” circuit on specific inputs. Refer to Level Protection on page 48 for a more detailed description.
4. If a system design requires a signal level to be maintained while not being actively driven, an external resistor or device must be used (Keepers assure no meta-stability of inputs but do not guarantee
a level).
5. The 750FX does not require external pullups on address and data lines. Control lines must be treated individually.