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TMPR3901F
230
4.7 Half-Speed Bus Mode
To accommodate slower peripheral circuits, the TMPR3901F offers a half-speed bus mode in which bus
operations are clocked at half the frequency of the R3900 Processor Core. This mode is selected by setting
the HALF* signal to low.
When HALF* is set to high, bus operations occur at the same frequency at which the R3900 Processor Core
operates. This is called full-speed bus mode.
When HALF* is asserted low, bus operations switch to half the frequency of R3900 Processor Core
operations. This is called half-speed bus mode.
In half-speed bus mode, the SYSCLK frequency is half that of full-speed bus mode. TMPR3901F bus
operations are always synchronized with SYSCLK.
Figure 4-9 shows a single read operation in half-speed bus mode.
The HALF* signal must be tied high or low. When changed dynamically, operation of the TMPR3901F is
undefined.
Figure 4-9 Single read operation in half-speed bus mode
Processor clock
A[31:2]
BE[3:0]*
RD*
BSTART*
ACK*
BUSERR*
D[31:0]
LAST*
SYSCLK