Rabbit 6000 User Manual page 342

The diagram below shows a PWM output for several different width values, for both modes of operation.
Operation in the spread mode reduces the filtering requirements on the PWM output in most cases.
The DMA channels on the Rabbit 6000 are designed to work with fixed I/O addresses. To allow DMA
control of the PWM, a separate PWM Block Access Register (PWBAR) and PWM Block Pointer Register
(PWBPR) are available. The pointer register contains the address of the PWM register to be accessed via
the access register. Each read or write of the access register automatically increments the pointer register
through the sequence shown below. Note that only the lower three bits of the pointer register actually
change. This allows the DMA to write to a fixed internal I/O location but still program all of the PWM
registers. The pointer register can be written and read if necessary. Normally the pointer register is initial-
ized to 0x88 (the first PWM register) and the DMA then transfers blocks of eight bytes to completely
reprogram the PWM.
0x88 -> 0x89 -> 0x8A -> 0x8B -> 0x8C -> 0x8D -> 0x8E -> 0x8F ->
When the DMA destination address is the PWBAR, the DMA request from the PWM is automatically
connected to the DMA.
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Rabbit 6000 User's Manual 342