TMPR3901F

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.

Processor clock

SYSCLK

A[31:2]

BE[3:0]*

RD*

BSTART*

LAST*

ACK*

BUSERR*

D[31:0]

Figure 4-9 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.

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Toshiba TX39 user manual Half-Speed Bus Mode, Single read operation in half-speed bus mode