
6-6
PowerPC Microprocessor Family: The Bus Interface for 32-Bit Microprocessors
Figure 6-3. 32-Bit Data Bus Transfer (Two-Beat Burst with DRTRY)
The 603 selects the data bus mode at start-up by sampling TLBISYNC at the negation of
HRESET. If TLBISYNC is asserted, the bus runs in 32-bit data mode; otherwise, it runs in
64-bit mode. If the TLBISYNC input function is not used, it can be connected to HRESET
to place the processor in 32-bit bus mode. Otherwise, it should be connected to a pull-up
resistor to select 64-bit mode. For systems using the TLBISYNC input function, HRESET
must be logically combined with TLBISYNC to select a data bus mode.
6.4 Reduced-Pinout Mode (603)
The 603 has an optional reduced-pinout mode. This mode idles the switching of numerous
signals for reduced power consumption. The DL[0–31], DP[0–7], AP[0–3], APE, DPE, and
RSRV signals are disabled when the reduced-pinout mode is selected. Note that the 32-bit
data bus mode is implicitly selected when the reduced-pinout mode is enabled.
When the 603 is in reduced-pinout mode, the bidirectional and output pins disabled are
always driven low during the periods when normally they would have been driven by the
603. The open-drain outputs (APE and DPE) are always three-stated. Bidirectional inputs
are always turned off at the input receivers of the 603 and are not sampled.
The 603 selects either full-pinout or reduced-pinout mode at start-up by sampling the state
of QACK at the negation of HRESET. If QACK is low at the negation of HRESET, full-
pinout mode is selected by the 603. If QACK is high at the negation of HRESET, reduced-
pinout mode is selected.
TS
ABB
A[0–31]
TBST
AACK
ARTRY
DBB
DH[0–31]
TA
DRTRY
TEA
0
1
0
1
2
3
4
5
6
7