
HX20 Technical NoteUsing the Trigonometric FunctionsThe HX20 has useful routines for SIN, COS, TAN and ATN built into the BASIC ROM. This technical note describes how to call them. 1. AddressesThe routines are located at the following addresses in Bank 0, (the internal bank of memory):
2. Floating point format usedThe routines are called with the following parameters:
Thus: an exponent of $7F = 2^1 Note also that an exponent of zero represents zero, regardless of the value of the mantissa. The mantissa is stored most significant byte first. The binary point is to the left of the most significant bit in $D5. All mantissas are between 0.5 and 1, and hence the most significant bit is always one. For example:
This representation is NOT the same as that used to store variables in BASIC, although it can be easily converted to that format. 3. ResultsThe routines return a result in the same format in locations $D5$D8 and $DD. Only bit 7 of location $DD is significant. Other locations from $80 to $FF may be altered. Note that the routines are NOT reentrant, and thus must not be called when BASIC is running, as BASIC uses the same areas of memory for all functions. 4. Example ProgramThe following code for my HX20 Assembler shows how to use the builtin trigonometric functions. 100 CLEAR 200,0:MEMSET&HB00:DEFINT AZ:FOR I=1 TO 2:GOSUB 180:NEXT I 110 A!=0:X=VARPTR(A!):POKE AADR,X\256:POKE AADR+1,X MOD 256 120 B!=0:X=VARPTR(B!):POKE BADR,X\256:POKE BADR+1,X MOD 256 130 INPUT "Value ";A! 140 EXEC DOATN 150 PRINT "ATN=";B! 160 GOTO 130 170 REM  180 ASM I 190 OBJ 200 HXATN EQU $C040 210 ; 220 FP EQU $D5 230 ; 240 FPSGN EQU $DD 250 ; 260 ORG $A49 270 AADR RDB 1 280 BADR RDB 1 290 ; 300 DOATN EQU * 310 CLR +$83 ;CLEAR PRECISION FLAG 320 LDA A #4 330 STA A +$85 ;4 BYTES FOR SINGLE REALS 340 LDX AADR 350 LDA A X+0 ;EXPONENT 360 STA A FP 370 LDA A X+1 ;MSB MANTISSA+SIGN 380 PSH A 390 ORA A #$80 ;SET MSB OF MANTISSA 400 STA A FP+1 410 PUL A 420 AND A #$80 ;SIGN FLAG 430 STA A FPSGN 440 LDA A X+2 ;MANTISSA 450 STA A FP+2 460 LDA A X+3 ;MANTISSA LSB 470 STA A FP+3 480 JSR HXATN 490 LDX BADR 500 LDA A FP ;MANTISSA+SIGN 510 STA A X+0 520 LDA A FP+1 ;MSB MANTISSA 530 AND A #$7F ;STRIP TOP BIT 540 LDA B FPSGN ;SIGN 550 AND B #$80 560 ABA ;COMBINE SIGN + MANTISSA 570 STA A X+1 580 LDA A FP+2 ;MANTISSA 590 STA A X+2 600 LDA A FP+3 ;LSB MANTISSA 610 STA A X+3 620 RTS 630 ASM OFF 640 RETURN Copyright © Julian Wald 2002 