Table 5-6. Input-Output Usage (Continued)
Input/Output with
Internal
Pullup Resistors
Required
External
Resistor
750FX Signal
Name
Input/
Output
Active Level
High
Usage Group
Level Protect
Comments
Notes
No resistor by
design
SYSCLK
Input
Clock Control
Keeper
Keeper
Active driver
3, 4, 5
3, 4, 5
TA
Low
High
Low
Input
Input
Data Termination
Active driver
TBEN
TBST
Input/Output
Transfer Attributes
JTAG
Keeper
1, 3, 4
5
External
pulldown
TCK
High
Input
Not enabled
Enabled high
5K Ω to GND
50µa@2.5V
25µa@1.8V
Internal
enabled
TDI
High
Input
JTAG
5
(the pullup current for the inter-
nal resistor)
TDO
High
Low
Low
Output
Input
JTAG
Data Termination
Control
Keeper
Keeper
Keeper
3, 4
3, 4, 5
3, 4
TEA
Active driver or pullup
Must be actively driven
TLBISYNC
Input
50µa@2.5V
25µa@1.8V
Internal
enabled
TMS
High
Low
Input
Input
JTAG
JTAG
Enabled high
Enabled high
5
(the pullup current for the inter-
nal resistor)
50µa@2.5V
25µa@1.8V
Internal
enabled
TRST
2, 5
(the pullup current for the inter-
nal resistor)
TS
Low
Input/Output
Output
Address Start
Keeper
Keeper
5K Ω
Pullup required to OV
3, 4, 5
1, 3, 4
DD
TSIZ[0:2]
Notes:
High
Transfer Attributes
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.
IBM [ IBM ]
