XC886/888CLM
Multiplication/Division Unit
User’s Manual
10-2
V1.3, 2010-02
MDU, V2.1
10.1
Functional Description
The MDU can be regarded as a special coprocessor for multiplication, division,
normalization and shift. Its operation can be divided into three phases (see
Phase one: Load MDx registers
In this phase, the operands are loaded into the MDU Operand (MDx) registers by the
CPU.
The type of calculation the MDU must perform is selected by writing a 4-bit opcode that
represents the required operation into the bit field MDUCON.OPCODE.
Phase two: Execute calculation
This phase commences only when the start bit MDUCON.START is set, which in turn
sets the busy flag. The start bit is automatically cleared in the next cycle.
During this phase, the MDU works on its own, in parallel with the CPU. The result of the
calculation is made available in the MDU Result (MRx) registers at the end of this phase.
Phase three: Read result from the MRx registers
In this final phase, the result is fetched from the MRx registers by the CPU. The MRx
registers will be overwritten at the start of the next calculation phase.
Figure 10-1
Operating phases of the MDU
Phase 1
Phase 2
Phase 3
Load Registers
Calculate
Read Registers
First Read
Last Read
Start bit is
set
First Write
Time
*
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