20-668-0024 Rabbit Semiconductor, 20-668-0024 Datasheet - Page 250

• Manufacturer Part Number: 20-668-0024
• Description: IC CPU RABBIT4000 128-LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 20-668-0024

• Processor Type: Rabbit 4000 8-bit
• Speed: 60MHz
• Voltage: 2.5V, 2.7V, 3V, 3.3V
• Mounting Type: Surface Mount
• Package / Case: 128-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Other names: 20-668-0022; 316-1078

The spreading function is implemented by dividing each 1024-clock cycle into four quad-
rants of 256 clocks each. Within each quadrant, the Pulse-Width Modulator uses the eight
MSBs of each pulse-width register to select the base width in each of the quadrants. This
is the equivalent to dividing the contents of the pulse-width register by four and using this
value in each quadrant. To get the exact high time, the Pulse-Width Modulator uses the
two LSBs of the pulse-width register to modify the high time in each quadrant according
to the table below. The “n/4” term is the base count, formed from the eight MSBs of the
pulse-width register.
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 4000 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
240
Pulse-Width LSBs
00
01
10
11
n/4 + 1
n/4 + 1
n/4 + 1
n/4 + 1
1st
n/4
n/4
n/4 + 1
n/4 + 1
2nd
Rabbit 4000 Microprocessor User’s Manual
n/4
n/4 + 1
n/4 + 1
n/4 + 1
3rd
n/4
n/4
n/4
n/4 + 1
4th