Digital PDFs

DIGITAL-8-14-U

December 2000

8 pages

Original

0.3MB

Document:	digital-8-14-u-d
Order Number:	DIGITAL-8-14-U
Revision:
Pages:	8
Original Filename:	https://svn.so-much-stuff.com/svn/trunk/pdp8/src/dec/digital-8-14-u/digital-8-14-u-d.pdf

OCR Text

IDENTIFICATION
I .I

DigifaI-8-I4-U—Sym

I.2

Binary to Binary Coded Decimal Conversion

I .3

March

I0, I965

PDP-B
LIBRARY

Digital-8— l4-U-Sym
Page 2
ABSTRACT

This subroutine provides the basic means of converting binary data to binary-

coded-decimal

(BCD) data for typeout, magnetic tape recording, etc.

REQUIREMENTS

3. 1

Storage
This subroutine uses 33 (decimal) storage locations.

3.3

Equipment
Standard PD P—8.

USAGE

4.2

Calling Sequence
The subroutine is called by the JMS instruction.

When called, the binary number

be converted must be in the accumulator (AC).
The subroutine will return to the instruction immediately following the calling

JMS with the BCD result in the AC.
6.

DESCRIPTION

6.l

Discussion

Reference to the Flow Chart (Section II. I) will illustrate this discussion.

pointer is initialized, the link is cleared
and a counter to control the number ofpasses through the computation loop proper is properly set.
On input the binary number is stored,

The loop is now entered.

It will be repeated eight times.

The binary equivalents of 800,

successively from the original

400, 200, IOO, 80, 40, 20, and IO are subtracted

binary number.

After each subtraction,

test on

the link is made.

If the result of the test shows

the link to be 0, the next lower equivalent is subtracted from the same quantity after the contents of the

links

(0) are shifted into the developing BCD number (Location NUMBER).

If the subtraction leaves a negative

link, the contents of the accumulator replace

the binary representation currently being processed after the contents of the link

been shifted into the growing BCD number.

(I) have

Digital-8— l4-U—Sym
Page 3
After eight poses through the basic loop, the developed BCD representation is
shifted left four bits and the "residual" least significant digit is added before exit.
6.2

Example
As an example consider the conversion of the binary equivalent of 5l2 decimal:
OOl 000 000 000

Successive calculations to obtain the most significant BCD digit are as follows:

Link

Addition
001 000 000 000
HO OH 100000

-800

lllOlllOOOOO
001 000 000 000

Hi 00] llOOOO
l

—400

000 CM HQ 000
000 OOl 110 000
ill llOOOl 000

—200

lllllllllOOO
000001 110000

111110011100
1

—100

000 000 001 100

Notice that the remainder is the binary representation of l2 decimal.

Writing

the link bits in the order they are developed gives OlOl the BCD character denoting 5.
6.3

Scaling

binary number must be no larger than 999 (decimal) which is equiva—
lent to l747 (octal). The binary point is assumed to be at the extreme right end of the word
(to the right of bit position ll) and the decimal point is also so positioned.
The original

In other words, this subroutine converts binary integers to BCD integers.

Note that the subroutine is designed for positive input only.'
7.

METHOD

7.2

Algorithm
The algorithm is straightforward and is fully described in sections 6. l , l0.4,

and ll

Digital-8- I4—U-Sym
Page 4
9.

EXECUTION TIME

9.I

Minimum
Minimum execution time will occur when the number to be converted is from 0

to 9

inclusively.

In this case, the execution time will be precisely 2l6.0 microseconds.

Maximum

9.2

Maximum execution time will occur when the number to be converted happens to

be 7.7X (decimal where X may represent any decimal digit).
microseconds
9.4

This time is precisely 235.2

Timing Equation
Execution time for a particular BCD result may be calculated from the following

formula,
TIME

2T6.0 + N x 3.2

where N represents the number of bits of the two most significant BCD digits that are equal

one.

For example, the binary equivalent of the decimal number 5I2 (0I0 I00 0I0 OIO)

will take exactly
2I6.0 + 3X3.2

225.6 microseconds

to convert.

IO.

PROGRAM

l0.4

Program Listing
A listing of the program with BCD located in 0200 appears as follows:

/BINARY TO BCD CONVERSION 3/6/65-DEC
/ENTER WITH BINARY NUMBER (<999(I0))
/IN ACCUMUIATOR; EXIT WITH THREE CHARACTER
/BCD NUMBER IN ACCUMULATOR
/AC 0-3; AC 4-7; AC 841 WILL CONTAIN
/THE BCD CHARACTERS. ON EXIT
AC 0-3 100
/WEIGHTING:
AC 4—7
To
/
AC 8-11
I
/
REGISTERS
/STORAGE 33(I 0)

Digital-8—14-U—Sym
Page 5

/T1ME=216.0-235.2 MICRO-SECONDS PDP—8
/lF INPUT >999 (10) RESULT IS UNSPECIFIED
0200

0000

0201

3226

DCAIhWUT

0202

1225

TAD CONTRL

0203

3210

DCA POINTR

0204

7100

(ILL

0205

1230

'DAD‘CCDUPJT

0206

3227

DCA NUMBER

0207

1226

TADIhWUT

0210

1231

BCD,

POINTR,

TAD TABLE

0211

7430

SZL.

0212

3226

DCAIhWUT

0213

7200

(ILA

0214

1227

TAD NUMBER

0215

7004

ILAL

0216

2210

ISZ POINTR

0217

7420

SPJL

0220

5206

JMP POINTR.-2

0221

7106

CLL RTL

0222

7006

RTL

0223

1226

0224

5600

TADIhWUT
JAAPI BCE)

1231

0226

0000

0227

0000

0230

0020

0231

6340

0232

7160

-0620

/OR TABLE+I, TABLE+2, ETC.
/|F C(L)=I, INPUT>—TABLE
/IFSO: INPUT=INPUT+TABLE
/PUT THIS BIT IN ANSWER
/UPDATE TABLE POINTER
/|F LINK=I, ALL DONE
/CONVERTED 2 BCD
/CHARACTERS
/SH|FT LEFT AND ADD
/THE THIRD

0
0

0020

/-800(10)
/—400
/—200
/- I 00
/—8O
/-40
/-20
/-10

—1440

0233

7470

-0310

0234

7634

-O144

0235

7660

—0120

0236

7730

0237

7754

-0050
-0024

0240

7766

-0012

/EXAMPLE:
/

/SET BIT 7:1; 8RAL'S
/WILL PUT IT IN LINK

'DAD LABLE

0225

CONRL
INPUT,
NUMBER,
COUNL
TABLE,

/STORE BINARY
/SET UP TABLE
/PO|NTERS

INPUT 0726 (8)
OUTPUT

0100/0111/0000

470 (10)

Digital-8—]4_U_Sym
Page 6
H.

11.1

Flow Chart

ENTER

DATA-DJNPUT

(C0NTR0L)+ POINTER

CLL

(COUNT)—>AC

(AC)—>NUMBER
TADINPUT

POINTER

TAD

(L)=o

TABLE

(L)=1

(AC)->|NPUT

CLA

T
TAD

NUMBER
CLL

RTL

CLL

RTL

RAL

ISZ

POINTER
TADINPUT

JMP

8CD

RETURN

(L)=o

JMP

PmNTER,q

(L)=1