Data Sheet
PowerPC® 750CXr RISC Microprocessor
Preliminary
6.4 Connection Recommendations
To ensure reliable operation, it is highly recommended to connect unused inputs to an appropriate signal
level. Unused active low inputs should be tied to OVDD. Unused active high inputs should be connected to
GND. All NC (no-connect) signals must remain unconnected.
Power and ground connections must be made to all external VDD, OVDD, and GND pins of the PowerPC
750CXr.
6.5 Output Buffer DC Impedance
The PowerPC 750CXr 60x drivers were characterized over various process, voltage, and temperature
conditions. To measure Z0, an external resistor is connected to the chip pad, either to OVDD or GND. Then
the value of the resistor is varied until the pad voltage is OVDD/2; see Figure 6-2 below.
The output impedance is actually the average of two resistances: the resistance of the pull-up and the
resistance of pull-down devices. When Data is held low, SW2 is closed (SW1 is open), and RN is trimmed
until Pad = OVDD/2. RN then becomes the resistance of the pull-down devices. When Data is held high, SW1
is closed (SW2 is open), and RP is trimmed until Pad = OVDD/2. RP then becomes the resistance of the pull-
up devices. With a properly designed driver RP and RN are close to each other in value, then Z0 = (RP +
RN)/2.
Figure 6-2. Driver Impedance Measurement
OVDD
RN
SW2
Pad
Data
SW1
RP
GND
System Design Information
Page 36 of 43
750cxr_DD4.0_Dev_gen_4_mkt.fm
February 28, 2005
IBM [ IBM ]
