Epson S1C63000 - Manual (Page 13)

S1C63000 CORE CPU MANUAL EPSON 7
CHAPTER 2: ARCHITECTURE
2.1.4 Arithmetic operations with numbering system
In the S1C63000, some instructions support a numbering system. These instructions are indicated with
the following notations in the instruction list.
ADC operand,n4
SBC operand,n4
INC operand,n4
DEC operand,n4
(See "Instruction List" or "Detailed Explanation of Instructions" for the contents of the operand.)
"n4" is a radix, and can be specified from 1 to 16. The additions/subtractions are done in the numbering
system with n4 as the radix. Various counters (such as binary, octal, decimal and hexadecimal) can be
realized easily by software.
The Z flag indicates that an operation result is "0" or not in arithmetics with any numbering system. The
C flag indicates a carry/borrow according to the radix.
The following shows examples of these operation.
Example 1) Octal addition ADC %B,%A,8 (C flag is "0" before operation)
Setting value Result F register
B register A register B register E I C Z
0010B(2) 0111B(7) 0001B(1) 0 – 1 0
0101B(5) 0011B(3) 0000B(0) 0 – 1 1
Example 2) Decimal subtractio SBC %B,%A,10 (C flag is "0" before operation)
Setting value Result F register
B register A register B register E I C Z
1001B(9) 0111B(7) 0010B(2) 0 – 0 0
0001B(1) 0010B(2) 1001B(9) 0 – 1 0
Example 3) 3-digit BCD down counter
LDB %EXT,0 ; Counter base address [0010H]
LD %XL,0x10
LDB [%X]+,0 ; Initial value setting [100]
LDB [%X]+,0
LDB [%X]+,1
:
:
CTDOWN: ; Count down subroutine----------
LDB %EXT,0 ; Counter base address [0010H]
LD %XL,0x10
DEC [%X]+,10 ; Decrements digit 1
SBC [%X]+,0,10 ; Decrements carry from digit 2
SBC [%X],0,10 ; Decrements carry from digit 3
CALR CTDISP ; Count number display routine
LD %A,0 ; Zero check
ADD %A,[%X]
ADD %X,-1
ADD %A,[%X]
ADD %X,-1
JRNZ CTEXIT ; Return if counter is not zero
CALR CTOVER ; Count over processing routine
CTEXIT:
RET
This routine constructs a 3-digit BCD counter using the decimal operation instructions underlined.
Calling the CTDOWN subroutine decrements the counter, and then returns to the main routine. If the
counter has to be zero, the CTOVER subroutine is called before returning to the main routine to
process the end of counting.