HPC46100 datasheet(29/32 Pages) NSC

29 / 32 page

Addressing Modes (Continued)

Double Register Indirect Using the B and X Registers

Used only with Reset Set IF and IF NOT bit instructions a

specific bit within the 64 kbyte address range is addressed

using the B and X registers The address of a byte of memo-

ry is formed by adding the contents of the B register to the

most significant 13 bits of the X register The specific bit to

be modified or tested within the byte of memory is selected

using the least significant 3 bits of register X

Code Efficiency

One of the most important criteria of a single chip microcon-

troller is code efficiency The more efficient the code the

more features that can be put on a chip The memory size

on a chip is fixed so if code is not efficient features may

have to be sacrificed or the programmer may have to buy a

larger more expensive version of the chip

The HPC46100 has been designed to be extremely code-ef-

ficient The HPC46100 looks very good in all the standard

coding benchmarks however it is not realistic to rely only

on benchmarks Many large jobs have been programmed

onto the HPC46100 and the code savings over other popu-

lar microcontrollers has been considerable Reasons for this

saving of code include the following

SINGLE BYTE INSTRUCTIONS

The majority of instructions on the HPC46100 are single-

byte There are two especially code-saving instructions JP

is a 1-byte jump True it can only jump within a range of plus

or minus 32 but many loops and decisions are often within

a small range of program memory

JSRP is a 1-byte call subroutine The user makes a table of

his 16 most frequently called subroutines and these calls

will only take one byte Most other micros require two and

even three bytes to call a subroutine The user does not

have to decide which subroutine addresses to put into his

table the assembler can give him this information

EFFICIENT SUBROUTINE CALLS

The 2-byte JSR instructions can call any subroutine within

plus or minus 1k of program memory

MULTIFUNCTION INSTRUCTION FOR DATA

MOVEMENT AND PROGRAM LOOPING

The HPC46100 has single-byte instructions that perform

multiple tasks For example the XS instruction will do the

following

1 Exchange A and memory pointed to by the B register

2 Increment or decrement the B register

3 Compare the B register to the K register

4 Generate a conditional skip if B has passed K

The value of this multipurpose instruction becomes evident

when looping through sequential areas of memory and exit-

ing when the loop is finished

BIT MANIPULATION INSTRUCTIONS

Any bit of memory IO or registers can be set reset or

tested by the single byte bit instructions The bits can be

addressed directly or indirectly Since all registers and IO

are mapped into the memory it is very easy to manipulate

specific bits to do efficient control

MULTIPLY AND DIVIDE INSTRUCTIONS

The HPC46100 has 16-bit multiply 16-bit by 16-bit divide

and 32-bit by 16-bit divide instructions This saves both

code and time Multiply and divide can use immediate data

or data from memory The ability to multiply and divide by

immediate data saves code since this function is often

needed for scaling base conversion computing indexes of

arrays etc

HPC46100 Datasheet(PDF) 29 Page - National Semiconductor (TI)

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