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Using Registers

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Using Registers

Ch.7 – p.158

Topic 1

PACKPDEC(3),ZDEC(3)

See page 159

Displacement Memory address distance from the most recent USING Length Number of bytesBase Register Established by BALR & USING. A program address is base + displacement

Example:AREG,ONHND(IXREG)

- The second operand is added to the first operand, and the sum in placed at the first-operand location. The operands and the sum are treated as 32-bit (for AH, second operand is treated as 16-bit) signed binary integers.
- When there is an overflow, the result is obtained by allowing any carry into the sign-bit position and ignoring any carry out of the sign-bit position, and condition code 3 is set. If the fixed-point-overflow mask is one, a program interrupt for fixed-point overflow occurs.
- 0no overflow1result < 0, no overflow2result > 0, no overflow3overflow

Example:SREG,ONORD(IREG)

- The second operand is subtracted from the first operand, and the difference is placed at the first-operand location. The operands and the difference are treated as 32-bit (SH, 2nd operand is treated as 16-bit) signed-binary integers.
- When there is an overflow, the result is obtained by allowing any carry into the sign-bit position and ignoring any carry out of the sign-bit position, and condition code 3 is set. If the fixed-point-overflow mask is one, a program interruption for fixed-point overflow occurs.
- 0result 0, no overflow1result < 0, no overflow2result > 0, no overflow3overflow

- The second word of the first operand (multiplicand) is multiplied by the second operand (multiplier), and the double-word product is placed at the first operand location. For M, the R1 field designates a even-odd pair of GPRs and must designate an even-numbered register, otherwise a specification exception is recognized.
- Both multiplicand and multiplier are treated as 32-bit (for MH, multiplier is treated as 16-bit) signed binary integers.
- No condition codes are set.

MR4,9

4

PRODUCT

5

MULTIPLICAND

PRODUCT

9

MULTIPLIER

- The double-word first operand (dividend) is divided by the second operand (divisor), and the remainder and the quotient are placed at the first operand location.
- The R1 field designates an even-odd pair of GPRs and must designate an even-numbered register, otherwise a specification exception is recognized.
- The dividend is treated as a 64-bit signed binary integer, The divisor, the remainder, and the quotient are treated as 32-bit signed binary integers. The remainder is placed in R1 and the quotient is placed in R1+1.

DR6,9

6

REMAINDER

7

QUOTIENT

9

DIVISOR

- The first operand is compared with the second operand, and the result is indicated in the condition code.
- The operands are treated as 32-bit signed binary integers
- 0operands are equal1first operand is low2first operand is high3- - - -

CR5,8

CWEEK-HRS,40HRS

- One is subtracted from the first operand, and the result is placed at the first-operand location. The first operand and result are treated as 32-bit binary integers with overflow ignored. When the result is zero, normal instruction execution sequencing proceeds with the updated instruction address. When the result is not zero, the instruction address in the current PSW is replaced by the branch address (the second operand).
- In the 2-byte format, if R2 operand is zero, no branch is taken, however one is still subtracted from R1
- The condition code is not used.

BCT3,LOOP

- Converts a Packed Decimal number to Binary
- Result is stored in the register (first operand)
- 2nd operand (B2,D2) must be 8 bytes

- CVBR1,D2(X2,B2)
- CVB7,PDECIMAL
- ---
- PDECIMALDCXL8’000000000000256F’

- Reverse of Convert to Binary
- Converts binary value in a register to packed decimal format and stores it in 8 bytes

- CVDR1,(D2(X2,B2)
- L6,HUNDRED
- CVD6,BINVALU
- - - - -
- BINVALUDSPL8
- HUNDREDDCF’256’*00 00 01 00

NUM is a 2-byte field with a value between 01 and 10. It is read in from an input file. It is used to index into a table with 10 different hourly salaries and NUM is consistent with the salary code number from a time-card.

NUM must be in binary format to be used as an index. Reg 7 contains the address on memory of the pay rate table (not shown) and each entry in the table is 5-bytes. The paycode is read in, PACKed and converted to binary. The appropriate table entry corresponding to the code is accessed and the pay rate is outputted to the monitor with a WTO instruction.

- Compare Logical Characters(CLC)
- 6-byte instruction format (SS)
- CLCD1(L,B1),D2(B2)
- Compare up to 256 characters

- Compare Logical Immediate(CLI)
- 4-byte instruction format (SI)
- CLID1(B1),I2
- Compare a single byte

- Different than arithmetic compare instructions – all characters are unsigned
- CLI compares a single byte in memory with a single byte that is included with the instruction (I2 field)
- CLC compares a byte at a time left-to-right (low-to-high)
- Both Compare instructions set the condition code

- Condition Code:
- 0operands are equal1first operand low2first operand high3- - -

CLIAB+10,C’C’

AB

D1 D6 C8 D5 E2 D6 D5 6B C1 4B C2 4B

AC

D1 D6 C8 D5 E2 D6 D5 6B C1 4B C3 4B

What is the CC that is set? ____________

1

- Move Characters(MVC)
- Move Immediate(MVI)
- Move Numerics(MVN)
- Move Zones(MVZ)
- Second operand is placed at the first operand location – left-to-right

- MVCD1(L,B1),D2(B2)
- Move up to 256 bytes from 2nd operand to the 1st operand
- Examples:
- MVCOUTAREA(80),INAREA
- MVCOUTPRICE(5),UNITCOST

- MVID1(B1),I2
- Moves a single character from the 2nd operand to the 1st operand
- 2nd operand is data within the instruction
- MVIOUTPRICE+0,c’$’

- Generally, used with zoned-decimal data – moves only the numeric part of the byte (not the zones)

FLDA

C6 C7 C8 C9

F0 F1 F2 F3 F4 F5

FLDB

MVNFLDB(4),FLDA

FLDA

C6 C7 C8 C9

FLDB

F6 F7 F8 F9 F4 F5

- Generally, used with zoned-decimal data – moves only the zones part of the byte (not the numerics)

FLDA

C6 C7 C8 C9

F0 F1 F2 F3 F4 F5

FLDB

MVZFLDB(4),FLDA

FLDA

C6 C7 C8 C9

FLDB

C0 C1 C2 C3 F4 F5

- Page 162 in your textbook
- Examples:
FWDCF’1’* 00 00 00 01 *HWDCH’123’* 00 78 *FWNDCF’-123’* FF FF FE DD*DWDSDFW4DS4FHW3DS3H

DCBADDDCA(INDCB)INBUFADDDCA(INBUFFER)

INDCB

INDCB

INBUFFER

INBUFFER

- Load Multiple (LM)
- Store Multiple(STM)

- Read Ch.7 – Topic 1
- But, you do not need to read the section called “Some System/370 Instructions” beginning on page 170 through the end of the Topic – page 175.
- But you can read the section if you want.

More About Binary Arithmetic

Ch.7

Topic 2

Page 176

- Let’s say you have a numeric value in a register, but you don’t know if it’s positive or negative. How can you tell?
- Is the number in the register above positive or negative? _______________
- How can you tell? _____________________________________

80 00 00 33

negative

High-order bit is set to one.

- Registers are 32 bits in length
- 31 bits are used to represent values
- High-order (left-most) bit is used to identify the sign
- Bit is “1” represents a negative value
- Number is in 2’s complement format (2’s complement format essentially is the bits are flipped – 1 bits become 0 and 0 bits become 1

FF FF FE DD

- High-order bit is “1” – value is negative
- Flip all the bits from 1 to 0 or from 0 to 1
- Then add 1
- Result is negative 123

00 00 01 22

00 00 01 23

- To convert a positive binary value:
- Subtract 1 from the original value
- Flip all the bits

=

00 00 01 23

FF FF FE DD

0000 0001 0010 0011

1111 1110 1101 1101

0000 0001 0010 0010

- 1

- If the value is in memory, use TM
- Test Under Mask instruction
- 4-byte format (SI)

- TM examines selected bits of a byte and sets the condition code
- 0selected bits are all zeros1selected bits mixed zeros & ones2- - -3selected bits are all ones
- What bits are examined?The 1-bits in the Mask field

TMVALUE,X’C1’MASK= 1100 0001

BZBITSOFFALL BITS OFF

BOBITSONALL BITS ON

BMBITSMIXDBITS ON AND OFF

:

VALUEDCXL4’E7B3C1F2’

Which branch is taken? _________________________

BITSON

- Using your Carlton Realtors program, change the decimal arithmetic to binary arithmetic accomplishing the same as you did using decimal arithmetic.
- Due: next week