S100 Computers CPM-86 Software

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A Collection of Useful Assembly Language Routines
Here is a growing collection of small but useful Z80, 8080 and 8086 Assembly Language routines I use time and time again in programs. Other donations will be gratefully received.

; BDOS EQUATES for running these routines under CPM

;

RDCON EQU 1 ;CP/M Read character

WRCON EQU 2 ;CP/M Write character

PRINT EQU 9 ;CP/M Print string

BDOS EQU 5

ESC EQU 1BH

CR EQU 0DH

LF EQU 0AH

; Main consol output routine using CPM.

; Character to be sent in [C].

; All registers unchanged

ZCO: PUSH AF

PUSH BC

PUSH DE

LD E,C

LD C,WRCON

CALL BDOS

POP DE

POP BC

POP AF

RET

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; Main consol input routine using CPM.

; Character returned in [A].

; All registers (except [A]) unchanged

ZCI: PUSH BC

PUSH DE

LD C,RDCON

CALL BDOS

POP DE

POP BC

RET

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; DISPLAY BIT PATTERN IN [A] (ZILOG, Z80)

; All registers unchanged

; The output will look like:- (10100110)

ZBITS:PUSH AF

PUSH BC

PUSH DE

PUSH AF

LD C,' '

CALL ZCO

LD C,'('

CALL ZCO

POP AF

LD E,A

LD B,8

BQ2: SLA E

LD A,18H

ADC A,A

LD C,A

CALL ZCO

DJNZ BQ2

LD C,')'

CALL ZCO

POP DE

POP BC

POP AF

RET

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; DISPLAY BIT PATTERN IN [A] (Intel, 8080)

; All registers unchanged

; The output will look like:- (10100110)

ZBITS:PUSH PSW

PUSH B

PUSH D

PUSH PSW

MVI C,' '

CALL ZCO

MVI C,'('

CALL ZCO

POP PSW

LD E,A

LD B,8

BITS2:MOV   A,E     ;There is no 8080 equivalent to the Z80's SLA E
      ANI   80H
      JZ    BITS4
      MVI   C,'1'
BITS3:CALL CO
      MOV   A,E
      RAL
      MOV   E,A
      DCR   B
      JNZ   BITS2
      JMP   BQ2
BITS4:MVI   C,'0'
      JMP   BITS3
BQ2: LD    C,')'

CALL ZCO

POP DE

POP BC

POP AF

RET

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; Obtain 2 HEX digits in [A] from keyboard

; If abort, Carry flag set & ESC is returned in [A]

; All registers unchanged except [A] (INTEL)

GETHEX:

PUSH B

MVI C,RDCON

CALL BDOS ;Get a character from keyboard & ECHO

CPI ESC

JZ HEXABORT

CPI '/' ;check 0-9, A-F

JC HEXABORT

CPI '9'+1

JNC HEXABORT

CALL ASBIN ;Convert to binary

RLC ;Shift to high nibble

RLC

MOV B,A ;Store it

PUSH B

MOV C,RDCON

CALL BDOS ;Get 2nd character from keyboard & ECHO

POP B

CPI ESC

JZ HEXABORT

CPI '/' ;check 0-9, A-F

JC HEXABORT

CPI '9'+1

JNC HEXABORT

CALL ASBIN ;Convert to binary

ORA B ;add in the first digit

ORA A ;To return NC

POP B

RET

;

HEXABORT:

STC ;Set Carry flag

MVI A,ESC

POP B

RET

; ;Convert LC to UC

UPPER:CPI 'a' ;must be >= lowercase a

RC ; else go back...

CPI 'z'+1 ;must be <= lowercase z

RNC ; else go back...

SUI 'a'-'A' ;subtract lowercase bias

RET

;

ASBIN:SUI 30H ;ASCII TO BINARY CONVERSION ROUTINE

CPI 0AH

SUI 07H

RET

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; DISPLAY CURRNT VALUE IN [A] (ZILOG)

; All registers unchanged

LBYTE:PUSH AF

PUSH BC

PUSH AF

RRCA

CALL CONV

CALL ZCO

POP AF

SF598:CALL CONV

CALL ZCO ;Send to consol

POP BC

POP AF

RET

;

CONV: AND 0FH ;CONVERT HEX TO ASCII

ADD A,90H

DAA

ADC A,40H

DAA

LD C,A

RET

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; DISPLAY CURRNT VALUE IN [A] (INTEL)

; All registers unchanged

LBYTE:PUSH PSW

PUSH B

PUSH PSW

RRC

CALL ZCONV

POP PSW

CALL ZCONV

MVI C,' '

CALL ZCO

POP B

POP PSW

RET

ZCONV:ANI 0FH ;HEX to ASCII and print it

ADI 90H

DAA

ACI 40H

DAA

MOV C,A

CALL ZCO

RET

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; Binary to ASCII Decimal String Conversion Print Routine

; [DE] contains binary number to be displayed as a decimal number.

; Note String is built right->left in buffer

; Then printed out via CPM. (ZILOG)

;

PRINT_DEC:

LD HL,BUFFER ;Location to hold string

LD (BUFPTR),HL ;Save buffer pointer

EX DE,HL

LD A,0

LD (CURLEN),A ;Current length of buffer is 0

LD A,H

LD (NGFLAG),A ;Save Sign Value

OR A ;Set FLAGS Value

JP P,CNVERT ;JMP IF VALYE IS +

EX DE,HL

LD HL,0

OR A ;CLEAR Carry

SBC HL,DE

;Convert Value to a String

CNVERT:

LD E,0 ;HL := HL DIV 10, DE := HL MOD 10

LD B,16

OR A

DVLOOP:

RL L ;Do a 24-bit shift left

RL H

RL E

LD A,E

SUB 10 ;If remainder is 10 or more next 1

CCF

JR NC,DECCNT

LD E,A

DECCNT:

DJNZ DVLOOP ;continue until all bits are done

RL L

RL H

CHINS:LD A,E ;Insert next character into buffer

ADD A,'0'

CALL INSERT

LD A,H

OR L

JR NZ,CNVERT

EXIT: LD A,(NGFLAG) ;All done

OR A ;Check it + or - overall

JP P,POS

LD A,'-'

CALL INSERT

POS: LD HL,BUFFER

LD A,(HL) ;number of characters in buffer

INC A

LD C,A

LD B,0

ADD HL,BC ;Point to end of buffer

LD (HL),'$' ;Put in terminating character for CPM

LD DE,BUFFER+1 ;Now print the complete string

LD C,PRINT ;(+1, because buffer count is in first posttion)

CALL BDOS

RET

INSERT:

PUSH HL ;Save for now

PUSH AF

LD HL,(BUFPTR) ;Current end of buffer

LD D,H

LD E,L

INC DE ;DE = End+1

LD (BUFPTR),DE

LD A,(CURLEN)

OR A

JR Z,EXITMR

LD C,A

LD B,0

LDDR ;Move entire buffer up one byte

EXITMR:

LD A,(CURLEN)

INC A

LD (CURLEN),A

LD (HL),A

EX DE,HL

POP AF

LD (HL),A

POP HL

RET

BUFPTR: DS 2 ;pointer to last character in buffer

CURLEN: DS 1 ;Current length

NGFLAG: DS 1

BUFFER: DB ' $' ;<<<<< Decimal string will be built here

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; Do a hexdump of the data in that is in a 512 byte (typically a BIOS DMA) buffer

; [HL] points to the buffer. Change values for [DE] below for different size buffers

; No registers modified (INTEL)

HEXDUMP:

PUSH PSW ;Save everything

PUSH D

PUSH H

CALL CRLF ;CR/LF first

MVI D,32 ;print 32 lines

MVI E,16 ;16 characters across

PUSH D

PUSH H ;Save the buffer location

;

SF172:CALL ZCRLF

SF175:CALL BLANK

MOV A,M

CALL LBYTE ;Display A on CRT/LCD

INX H

DCR E

JNZ SF175

MVI E,16

DCR D

JNZ SF172

;

CALL ZCRLF

POP H ;Get buffer address again

POP D ;Get chars/line again

;

XF172:CALL ZCRLF ;Now show as ascii

XF175:CALL BLANK ;send a space character

MOV A,M

ANI 7FH

CPI ' ' ;FILTER OUT CONTROL CHARACTERS

JNC XT33

XT22: MVI A,'.'

XT33: CPI 07CH

JNC XT22

MOV C,A ;SET UP TO SEND

CALL ZCO

INX H

DCR E

JNZ XF175

MVI E,16

DCR D

JNZ XF172

CALL ZCRLF

POP H

POP D

POP B

POP PSW

RET

;

BLANK:MVI C,' '

CALL ZCO

RET

;

ZCRLF:MVI C,CR

CALL ZCO

MVI C,LF

CALL ZCO

RET

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;Convert BCD number (Two digits only) in A to Binary
;No registers modified (INTEL)

BCDTOBIN:
       PUSH B
       PUSH D
       MOV   B,A   ;Save it
       ANI   0FH   ;Mask most significant four bits
       MOV   C,A   ;Save unpacked BCDI in C register
       MOV   A,B   ;Get BCD again
       ANI   0F0H ;Mask least significant four bits
       RRC       ;Convert most significant four bits into unpacked BCD2
       RRC
       RRC
       RRC
       MOV   B,A   ;Save unpacked BCD2 in B register
       XRA   A     ;Clear accumulator (sum = 0)
       MVI   D,0AH ;Set D as a multiplier of 10
Sum:   ADD   D     ;Add 10 until (B) = 0
       DCR   B     ;Decrement BCD2 by one
       JNZ   Sum   ;Is multiplication complete? i if not, go back and add again
       ADD   C     ;Add BCD1
       POP   D
       POP   B
       RET       ;Return with binary value in [A]

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;Generalized Subroutine to convert binary number in [A] into its equivalent BCD number ;stored in RAM. Will return right most 2 digits in [A]
;No registers modified (INTEL)

BINTOBCD:              ;Convert binary number in [A] to BCD in RAM
        PUSH   B       ;Save BC register pair contents
        PUSH   D       ;Save DE register pair contents
        MVI    B,64H   ;Load divisor decimal 100 in B register
        MVI    C,0AH   ;Load divisor decimal 10 in C register
        MVI    D,00H   ;Initialize Digit 1
        MVI    E,00H   ;Initialize Digit 2
STEP1: CMP    B       ;Check if number < Decimal 100
        JC     STEP2   ;if yes go to step 2
        SUB    B       ;Subtract decimal 100
        INR    E       ;update quotient
        JMP    STEP1   ;go to step 1
STEP2: CMP    C       ;Check if number < Decimal 10
        JC     STEP3   ;if yes go to step 3
        SUB    C       ;Subtract decimal 10
        INR    D       ;Update quotient
        JMP    STEP2   ;Continue division by 10
STEP3: STA    Digit0 ;Store Digit 0
        MOV    A,D     ;Get Digit 1
        STA    Digit1 ;Store Digit 1
        RLC            ;Shift it up 4 bits
        RLC
        RLC
        RLC
        ANI    0F0H
        MOV    D,A     ;Temp store in D
        MOV    A,E     ;Get Digit 2
        STA    Digit2 ;Store Digit 2
        LDA    Digit0
        ORA    D       ;Add in 10's digit
        POP    D       ;Restore DE register pair
        POP    B       ;Restore BC register pair
        RET            ;Return to main program

Digit0: DB 0           ;Store for Bin->BCD
Digit1: DB 0
Digit2: DB 0

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This page was last modified on 05/14/2016