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2.3
CPU Registers
2
The F
MC-16LX registers are divided into special registers inside CPU and general-
purpose registers on memory. The former is dedicated hardware inside the CPU, and
its use is limited because of the CPU architecture. The latter shares CPU address
spaces with RAM. A general-purpose register can also be accessed without
specifying an address, but a user can specify the use of a general-purpose register,
which is the same as for memory spaces.
■
Dedicated registers
2
The F
MC-16LX has the following 11 types of dedicated registers:
•
Accumulator (A = AH: AL)
•
User stack pointer (USP)
•
System stack pointer (SSP)
•
Processor status (PS)
•
Program counter (PC)
•
Direct page register (DPR)
•
Program counter bank register (PCB) : 8-bit register indicating a PC space
•
Data bank register (DTB)
•
User stack bank register (USB)
•
System stack bank register (SSB)
•
Additional data bank register (ADB)
Figure 2.3-1 shows the configuration of the dedicated registers.
Figure 2.3-1 Configuration of dedicated registers
AH
AL
USP
SSP
PS
PC
DPR
PCB
DTB
USB
SSB
ADB
8 bits
16 bits
32 bits
: Two 16-bit accumulators
(used as single 32-bit accumulator)
: 16-bit pointer pointing to user stack area
: 16-bit pointer pointing to system stack area
: 16-bit register indicating system status
: 16-bit register containing a program address
: 8-bit register indicating a direct page
: 8-bit register indicating a DT space
: 8-bit register indicating a user stack space
: 8-bit register indicating a system stack space
: 8-bit register indicating an AD space
Accumulator
User stack pointer
System stack pointer
Processor status
Program counter
Direct page register
Program counter bank register
Data bank register
User stack bank register
System stack bank register
Additional data bank register
CHAPTER 2 CPU
29
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