Datasheet

C161S
Functional Description
Data Sheet 13 V1.0, 2003-11
3.3 Central Processing Unit (CPU)
The main core of the CPU consists of a 4-stage instruction pipeline, a 16-bit arithmetic
and logic unit (ALU) and dedicated SFRs. Additional hardware has been spent for a
separate multiply and divide unit, a bit-mask generator and a barrel shifter.
Based on these hardware provisions, most of the C161S’s instructions can be executed
in just one machine cycle which requires 100 ns at 20 MHz CPU clock. For example,
shift and rotate instructions are always processed during one machine cycle
independent of the number of bits to be shifted. All multiple-cycle instructions have been
optimized so that they can be executed very fast as well: branches in 2 cycles, a
16
× 16 bit multiplication in 5 cycles and a 32-/16-bit division in 10 cycles. Another
pipeline optimization, the so-called ‘Jump Cache’, allows reducing the execution time of
repeatedly performed jumps in a loop from 2 cycles to 1 cycle.
Figure 4 CPU Block Diagram
The CPU has a register context consisting of up to 16 wordwide GPRs at its disposal.
These 16 GPRs are physically allocated within the on-chip RAM area. A Context Pointer
(CP) register determines the base address of the active register bank to be accessed by
the CPU at any time. The number of register banks is only restricted by the available
internal RAM space. For easy parameter passing, a register bank may overlap others.
MCB02147
CPU
SP
STKOV
STKUN
Instr. Reg.
Instr. Ptr.
Exec. Unit
4-Stage
Pipeline
MDH
MDL
PSW
SYSCON
Context Ptr.
Mul/Div-HW
R15
R0
General
Purpose
Registers
Bit-Mask Gen
Barrel - Shifter
ALU
(16-bit)
Data Page Ptr. Code Seg. Ptr.
Internal
RAM
R15
R0
ROM
16
16
32
BUSCON 0
BUSCON 1
BUSCON 2
BUSCON 3
BUSCON 4 ADDRSEL 4
ADDRSEL 3
ADDRSEL 2
ADDRSEL 1